I used to like Unity+Compiz's eyecandy but switched away because it was causing lockups on my rather old, nvidia-powered desktop. Tiling WMs are for people who want to live away from the mouse as much as possible -- and who think, in particular, that dragging window borders with a mouse is not fun. And a side benefit is it maximises your screen real estate. And it's lightweight -- much lighter than even XFCE. On an old machine, the speed difference is striking.