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.
To get the normal KWin title bar to appear, go into System Settings, Window Behavior, Window Specific, then New...
Click the Detect Window Properties button and then click an open Chromium window to fill in the details, as in this screenshot.
(Note that for most apps you can right-click the title bar of the window, go to Advanced and Special Application settings and get to the same place, but in the special case of windows without normal title bars, you have to do it in this more roundabout way.)
Then go to Preferences and set No Border to "Force", and uncheck the box. (This is kind of confusing because it's a double-negative; a checked box means to hide the window borders, and an unchecked box means to show them.)
Once you save and apply all of this, Chromium will have a normal window title and border forever, whether it likes it or not. Rejoice as sanity is restored to the world.
You can use this dialog to do other helpful things like make your IM windows be sticky across all desktops by default. Or to sort your applications to always start (and stay) on certain desktops. Or to force applications to start maximized or have a certain geometry.
Another thing I find very helpful is to turn Focus stealing prevention to the highest setting for any program that likes to throw dialog boxes at me and demand immediate attention. Thunderbird used to be really annoying in this way.
Most other Linux window managers can do some of this kind of thing too with either built-in options or via 3rd-party scripts (last I checked Gnome was the latter but it's been a while). However few do it as well as KWin. The only thing I've used comparable to KWin is probably FVWM, and KWin's GUI configuration is orders of magnitude easier to work with than FVWM config files.