It used to be common practice to occasionally run a clean install, and then manually migrate all the files and settings over in order to get a completely fresh start.
That will make your Mac run blazingly fast for a few months or more, and many people report that it fixes longstanding problems they’ve had too. When you install a new major version of OS X, or after some time has passed, it is a good idea to do a clean install (that is, to erase the disk you are installing OS X onto as part of the installation process).
