Would the "Icon only" task manager perhaps suit you better?

Created attachment 94102 [details]
Right size for the windows for me.

Created attachment 94103 [details]
Too wide for me.

Created attachment 94104 [details]
side by side

No, I prefer the classique taskbar with the windows, not just the icons.
I joined some screenshot to show what I mean. 

The first (black taskbar) is from plasma 4 with expanding icon taskmanager. This is what I use and I find it's the width perfect.

The second is from plasma 5 with task manager. The size is too wide.

Expanding icon taskmanager isn't available on Kubuntu (https://bugs.launchpad.net/ubuntu/+source/kubuntu-meta/+bug/1480362) and I would prefer to use the "standard" taskbar. 

I think some people prefer to have the windows with small width whereas some others prefer to have them wide. So an option to choose the size (small, medium, large) will be much appreciated.

They automatically shrink as you open more windows.
What's the advantage of an option?

I know but if you have, let say, 4 windows opened on a 23" 1080p they don't shrink.

Like I said, it force you to make a little more distance with the mouse each time you switch windows and it's annoying when you do that all day/week/year.

The perfect size for me is like on the first attachment.

I've tagged the VDG/Usability team for comments

That actually does sound like a matter of personal preference - and therefore a good case for an option - to me.

It should not just be added to the already quite long "General" settings page, though. I'd recommend splitting the settings into "Layout" (which would contain the "Arrangement", "Grouping" and the new "Task width" option) and "Behavior" (which would contain the current "Behavior" group plus the "Filters" group.

I definitely won't add an option for this.

(In reply to Eike Hein from comment #10)
> I definitely won't add an option for this.

It's fine if you disagree witht he proposed solution to the problem "Wide taskbar entries require unnecessary moue travek when switching windows", but in that case we'd need an alternative solution to the problem.
Any idea?

I don't buy the argument that it does.

Usage of the task bar is you move the mouse from where it is on the screen in the application to *an* item of the taskbar. 
If your mouse happens to be on the right of the screen and you want to activate the window that happens to be on the right of the taskbar, having them smaller actually makes it worse.

As David says, strictly horizontal pointer movement between distinct task delegates in the bar for the purpose of multiple activations in a row is a relatively rare usage pattern. Much more frequent is aiming for a particular delegate from an arbitrary screen coordinate at an angle to the target, in which case a larger target actually helps (Fitts' Law).

That is where different usage patterns come into play. If the pattern is "Do something in an application, switch, do something in another application, switch again, ..." (which arguably is the most common pattern), then yes, wider hit targets are indeed the preferred choice. Actually, the optimum option for this would be to just divide the task bar by the number of tasks and not limit the width at all, but that might have negative aesthetical implications (i.e. "it might look weird").

However, in a workflow where the user has to frequently switch between applications without actually interacting with them (e.g. a monitoring task where the individual windows are too big to place them side by side), narrower tasks would be preferable.

We should hear the reporter out about which workflows he finds the wider taskbar entries to decrease efficiency before jumping to conclusions.

So, Jeremy, could you please tell us what it is that you're doing with your computer where you'd wish to have narrower taskbar entries?

> but that might have negative aesthetical implications (i.e. "it might look weird")

Having an upper bound on the scaling range avoids movement in more situations, which is nice to avoid UI busyness and having to retarget when monitoring a delegate label for changes. (Incidentally wider buttons also allow fitting more text.)

Also, switching between two applications repeatedly can be easily achieved by tapping Alt+Tab once which always switches to the previous window.

IMO the option suggested by jeremy9856 should be added 'cause a lot of users (like me) use "Icon-only task manager" plasmoid exactly for this reason: if you have only icons you can quickly switch windows to i.e. check apps' status or to find the window you're searching for.
So in my humble opinion it's important to provide an additional option to the users: with size-reduced "icon+title" task manager plasmoid the user can view (a preview of) window's titles (not possible with icon-only tm) and also switch windows with a little movement of the cursor.

As I said, a wide sized windows switcher is not sustainable because you need to make more movement to switch windows. 

About my workflow, I like to have only one window on the desktop and the others minimized. To minimize / unminimized them I use the taskbar switcher and I use it a lot. It's certainly not the best workflow but it's mine.

The icon view is not sustainable because it miss the windows titles to, for instance, quickly find the window you're searching for and I don't use Alt+Tab.

That's why, like Alex L (you see I'm not alone), I use "Icon-only task manager" to have a "normal" sized taskbar switcher.

If you take a look at every other "classical" desktop environements (Xfce, Cinnamon, Mate, Lxde, Budgie), "Icon-only task manager" or even at Windows, they have all a "standard" sized taskbar switcher.

We don't ask something big, just a little option to select the right sized taskbar switcher for us.

I prefer to have the choice but If you really don't want to add an option you can simply make the windows width smaller like on every others desktop :

http://r3dux.org/wp-content/uploads/2011/08/r3dux-XFCE-Desktop-Web.jpg

https://spins.fedoraproject.org/static/images/screenshots/screenshot-lxde.jpg

http://multimonitorcomputer.com/solved/images/windows-7-speaker-icon-taskbar.jpg

http://www.winbeta.org/sites/default/files/styles/watermark/public/news/Transparencyeffect61.jpg?itok=SVKzJhum

http://img.clubic.com/07895117-photo-windowsxp.jpg

http://i.ytimg.com/vi/wmvvld118Xw/maxresdefault.jpg

http://www.abclinuxu.cz/images/screenshots/0/5/185850-mate-desktop-1649455225982173549.jpg

http://i1-news.softpedia-static.com/images/news2/Beautiful-Budgie-Desktop-Environment-Receives-Massive-Update-457583-4.jpg

Git commit f34cf61260ab02dfda4da0cb1368d853df306246 by Eike Hein.
Committed on 30/09/2015 at 13:43.
Pushed by hein into branch 'master'.

Reduce maximum preferred size for task delegates a little.

There's been repeated feedback they're too wide by default.
Related: bug 353337

M  +1    -1    applets/taskmanager/package/contents/code/layout.js

http://commits.kde.org/plasma-desktop/f34cf61260ab02dfda4da0cb1368d853df306246

Thank you

I really don't want to abuse but it's still a little bit to wide I think. For a 1080p screen, the original size was 327px and now it's 303px. The size I like is 185px but it's maybe a little too small to please everyone.

I made some test and I propose to set the size at about 230px. It's a good compromise, not too big and not too small, and correspond with the others desktop environments. It should be something like that by seeing the patch you made (a really easy fix !) :

return Math.floor(preferredMinWidth() * 1.2);

Thank you very much

Hello Eike Hein,
Can you make it a little more smaller please ?
Thanks !

I don't know it's not so bad now. A little bit smaller will be better perhaps ?

With Plasma 5.5.1 and KF 5.17 the size of the window is about 250px on Manjaro and I think it's a good compromise. Thanks !