Is it a good idea to reinstall OS X from time to time?

Episode 1152 (36:20)

Ken from Cape Girardeau, MS
Apple iMac

Ken has a old Intel iMac. Should he be reinstalling OS X occasionally to keep it running well? Leo says that he could, but it's not as important on a Mac as a Windows PC. This is largely because it doesn't have a registry. But he can do it if he wants, and it's really easy to do now. Once a year or two, it's a good idea to clear out the machine and start over. He should just make sure to back up his data first though.