I believe that most of us have Macs with enough power for Mac OS X to run smoothly, but if you have speed problems with the Mac This is a very interesting solution, and it is that the shadows consume a lot of CPU for rendering.
For this we can use Shadowkiller, a utility that allows to eliminate the shadows of the interface and therefore gain in fluidity and speed, although logically we lose in visual aspect.
It is your decision to decide what is more important to you, as long as your Mac is not running smoothly, something that is not usual anyway.
Source | OS X Daily