This has been in my head for quite some time: In System settings we have "pages" where 90% of the space is grey, and the window size does not change dependent of the module loaded at the moment.
Another example would be password dialogs: Who needs to maximize a password dialog? This just leads to bad alignment, no matter how good your initial design was.
The problem with this idea is: If we would introduce maximal window sizes, many people would complain, as it may break their workflow, with tiling window managers for example (even if it is still not useful to resize a password dialog).

So my thought would be: Maybe it would be useful to introduce a change of the window size if system settings modules are opened, depending on how much space would be necessary to display its content ideally.

This thought is a very controversial idea and I think many people will be against it, but I just want to know what you think? I am not sure about it myself.
Maybe Kwin maintainer Martin Gräßlin should be asked what he thinks this would mean for him from a window manager devs perspective.

Yes this is indeed a very controversial idea. In my opinion, randomly changing the window size when I click buttons inside a window is on the top three list of things a program absolutely must never do. It is extremely distracting.

Well I can agree that child windows (like your example - the log-in window) could be constricted in size or simply not be using the same rules and decorations as other windows (for an example of the issues from a usability standpoint, try the settings windows for Plasma Netbook in systemsettings or the crash-warnings) - there is a thread here in the VDG-forum about a new theme engine that has some bits about that, you should check it out.

But aside from that that may be tricky to do in a good way so it wouldn't simply trash most users way of interacting with the desktop.

Could you show us some sketches or examples of what you mean to sort of get the ball rolling and talk more about this idea?

Jens: I agree about the child window thing. Locking the window size should not be used for primary windows of course!

To extend my point further about System settings: Something like that can be seen in the linked video (In this case Wacom tablet settings are clicked and the window resizes.)
http://youtu.be/rsSV33XxePk?t=7s

In the linked video this does not make that much sense (because the window would be fine, even if the space was not removed, but I can think of some cases it may look better if the size is adjusted.
But again, I am not sure about this idea myself and there is the potential that it annoys users. Apart from that, the linked Gnome Settings are in a completely other situation, as they are pretty minimal, and do not have submodules in each module, so this could indeed get messy in case of KDE.

If you think it is a bad idea, please state so and we will forget about this idea.

If you think it is a bad idea, please state so and we will forget about this idea.

Hehe, lets say I'm a tad sceptical of how good it would be but I also think that some ideas that at first seems completely insane may turn out to be incredible in the end, either through tweaking or by explaining the idea further. Even if it doesn't work it might bring out other ideas.

I'd rather see ten weird concepts too many expanded and worked through than one perfect one missed because it was discredited without thought.

So if you feel like it I would love to see more (I'm doing the dishes and cooking food right now and still have the darn animations in another thread to finish so I can't give proper feedback for a while just FYI) - if you're afraid you might be wasting time and prefer to drop it, that's of course up to you.

I don't think the idea is necessary bad, but I think the main problem we would have (as far as the system settings anyway as some modules don't have much content) is that the windows would vary in size by so much it would be too distracting. Unless you set a minimum size and just expanded if one or two modules needed extra room to show their settings? But if it would only be one or two modules that needed it, would it be worth the effort to implement?

Hmm, thinking about it more it might work if there were a user defined minimum AND maximum size the window could be allowed to expand to. For example, I've just opened a window and it has an almost pointless scrollbar to scroll about 0.5cm, so in that case I think it would be useful for the window to auto-expand to get rid of the scroll bar.

Well windows expanding when the contents don't fit is what it works like right now, assuming the contents don't allow scrolling. And it's already kind of horrible when it happens because everything jumps around.

I still believe managing windows should be left to the window manager. Applications shouldn't try to do the window manager's job by resizing windows as they think the user wants them to be. Same goes for limiting the maximum size: why would you do that, even for a message box? The toolkit supports it. You can just set a sane default size and everything is fine. And if a user wants to expand a message box, let him do it -- he'll have a reason to do so! Some message boxes have lots of text for example and it might be more convenient to read it in a larger box.

Greetings,
Sven