That's a good habit to be in, especially if you are experiencing issues and don't know what is causing them. I also clear my history automatically by selecting that in my Firefox options. No
sense in keeping scads of little temp files and long lists of browsing results either. The less your CPU has to do in the way of housekeeping, the better.
You can also accomplish that by using one of the eraser/disk cleanup programs. They also erase temp files. Spybot asks you about temp files when it runs and will clear them out if you let it. It also removes any adware or spyware that has crept into your system. Those can eat a few CPU cycles and some are inherently dangerous in terms of security.