Probably true but it comes down to if it takes more time to take care of it or to spend some time to make a full reinstall.
Setting up a Scheduled disk defrag is a one-time 15 minutes task at most.
Cleaning up Registry via a Registry Cleaner type of program is ~ 2 minutes a month.
Cleaning out Win TMP directory is ~ 0.5 minute a month.
Cleaning out Win Uninstall Dirs is ~ 0.5 minute a month.
How long is your typical reformat and redo a full install with reinstalling all of your software and tweaking all of your OS settings back to the way they were?