SUMMARY
I notice that some SystemSettings modules uses Tooltip, some other uses "What's This?" instead. We have no consistency, but I mainly think that we should avoid using "What's This?" in a configuration module, because:

- the informations they can carry are meant to help users, but with tooltip one can have them right away;
- I'm not sure all the users know how "What's This?" can be triggered; if this is true, these informations are simply unuseful;
- "What's This?" are a sort of "treasure hunt" for me, since its not visually clear if there are or not, and what they are related to, so you have to clic all over the page; with tooltip you have just to hover.

STEPS TO REPRODUCE
1. Go in the "Windows Behavior" tab and trigger the "What's This?" help: you'll get some useful informations ("Here you can customize the way windows behave when being moved, resized or clicked on. You can also..."), but these informations could be placed directy at the top the module (this was done in "Night Color" module).
2. If you remain in this module you'll see that nearly all the options have a the "What's This?" help, but it's not visually obvious;
3. Go in the next module, Switcher: tooltips are used here (and I think this is good).
4. And so on...

OBSERVED RESULT
There is no a rule, sometimes "What's This?" is used, sometimes Tooltip is used instead. "What's This?" is not so handy in a configuration module, imho.

EXPECTED RESULT
A little description at the top of each module could be welcome (e.g. see the "Night Color" module). I think also that in the settings pages we should always use tooltip instead of "What's This?", because:

-users should have all the informations available right away;
-perhaps most of them don't know how to trigger a "What's This?" help.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.18.4
KDE Frameworks Version: 5.69.0
Qt Version: 5.14.1

ADDITIONAL INFORMATION