I don't believe hines232 is talking about defragmenting the HDD but using scandisk (A.K.A. chkdsk) to check for hard disk errors (though I could be wrong) and repair any bad sectors, etc.
@ hines232, if my assumption is correct:
I would only do this if I kept getting unexplained errors, crashes, etc. and was unable to identify a cause, it isn't something that I would do on a regular basis. I can't recall when I did one last, years ago would be about right.