i usually do it every few weeks, till recently when my
system hung during it and windows wouldn't boot
but unless you constatly add and remove things once every
2 or 3 weeks will be sufficient plus if you just analyze
it it will tell you whether it needs it or not,listen to
it, and make sure you have nothing open when running it
or else.....(system hung during it and windows wouldn't
boot) good luck hope that helps Cliff