KDE is awesome largely because KWin is awesome. If I had to name one reason I gave up using Gnome and moved to KDE, it'd be KWin.

Some programs (for example, Songbird, aTunes, Google Chrom(e|ium)) try to manage their own windows in silly ways like hiding their title bars and window borders, or fiddling with how they appear in pagers or task managers / application lists, or trying to manage their own sizes and positions. KWin lets you override and force sane preferences upon such programs.

Chromium for Linux is nice enough to give you an option to "Use system title bar and borders" if you right-click the top. But this only changes how Chrome looks; it doesn't make the KWin title bar and borders appear.

Why would you want KWin title bar and borders? Because by default, Chromium's self-managed title bar only gives you Windowsy options like minimize/maximize/close. It doesn't give you Linuxy options like double-clicking the title bar to window-shade the window, or right-clicking the title bar to get the KDE menu to send it between desktops or make it Always on Top, and such goodness. If I wanted gimped up window management I'd go use Windows 95.