This was my original response to this question:
Through the course of work on a computer, installing and removing
applications, etc. it is not unusual to end up with invalid entries in
the registry. Unlike Windows 9x, I personally have seen no need to use
registry cleaners nor any evidence of major slowdowns caused by such
entries from normal use. If you've had viruses or malware of some type
that you've had to clear from your system, it's possible they may have
left entries that might be causing some problems but under normal use,
I've rarely seen slowdowns caused by the registry. Your mileage may
vary, some of it depends upon your usage, what you have installed, how
recent are these applications as in are they XP apps or 9x apps or
older apps which might gum up the registry.
Is it safe to let a program like this fix all registry entries? It's
not SAFE to let any such program make changes in the registry and it's
not safe to be rooting around in the registry at all, period. Any time
you do so, you should be well backed up and be prepared for a situation
where your system becomes unbootable, in other words, some sort of
means for a quick restore such as an image of your current setup to
which you can quickly return.
--
Michael Solomon MS-MVP
Windows Shell/User
Backup is a PC User's Best Friend
DTS-L.Org:
http://www.dts-l.org/