Compositors are not just about visual effects. They are also a pretty good way to leverage GPUs. If you don't care that much about latency, there's a clear ben

Compositors are not just about visual effects. They are also a pretty good way to leverage GPUs. If you don't care that much about latency, there's a clear benefit in never having windows getting "damaged" just because other stuff has temporarily occluded them. You will never get "ghost" images because one app has locked up or is slow. No flurry of "WM_PAINT", "WM_NCPAINT" or whatever equivalent just because you are moving windows. No matter how fast your system is, any 'movement' is much more fluid (as position changes are almost free). Essentially, having windows completely isolated from one another - except when they are "composited" back - simplifies a lot. There's a lot of cruft and corner cases that you don't have to care. There are features that can enhance usability that are trivial to do with compositors but difficult without - for instance, showing a window "preview" when you are switching apps or when you mouse over in the taskbar. While you can do this without a compositor, you can get this very easily and for almost 'free'. And, as you point out, you can post-process and apply whatever effects you want. But this is a minor detail and was used initially as a selling point. Of course, for a tiling window manager none of this matters as they never overlap. But most users don't use tiling window managers.