In the previous applet I believe, but also something that I use personally was to exactly type where each monitor should be placed. Now you drag the monitors around but its hard to get somewhat precise. Nvidia settings pretty much nailed it I think. Reproducible: Always
Created attachment 95414 [details] shows the nvidia-settings coordinate settings. This shows the nvidia settings window that I think pretty much nailed it when it comes to monitor placement settings.
Wanted to add, a common usecase on to why you don't want to have each monitor bezel to bezel when setting up monitors is when you want to have some form of bezel compensation. Feels a bit more natural when moving windows across but also when using whole desktop to make the picture look better. Bezel compensation; http://www.nvidia.com/props/IO/127135/761/bezel-correction.jpg In current state you cannot do that in kscreen since moving mouse it snapps to the other display. Adding that you can manually type the coordinate for each display gives more control and also enables this. Another feature would also be by during keypress ctrl or other key the snapping turns off giving you more precise control with mouse when placing monitor. (But that is probably another feature request).
*** Bug 452190 has been marked as a duplicate of this bug. ***
*** Bug 425799 has been marked as a duplicate of this bug. ***
Agreed this is needed until snap-to alignment of displays gets better do disallow improper overlap. Right now aligning displays is extremely tedious with smaller windows in a 4k hidpi situation. Using nvidia-settings as an example of what to do in aligning displays and snapping to should be an example of how to behave. I use nvidia-settings in doing so most times when I have to just to save sanity from KDE settings.