Registry cleaners sell themselves on the idea that programs leave behind a lot of junk in the Windows registry. They claim that by running their utility, the old unused entries get deleted, thus streamlining your registry.

In our forums, arraknid put it nicely:

"It is true that uninstalled programs have a habit of leaving redundant entries behind which will eventually clutter the Registry, and cleaning it from time to time can only help. Whether it speeds up the operating system is debatable."

The Windows Registry works like a document filing system - the software knows what entry it is looking for and can find the entry quickly just by looking in the right place. It doesn't matter if there are hundreds or thousands of entries, because it knows the exact location of where to find the information it needs. Therefore, removing excess entries and slimming down the registry will give you no performance gain. Countless studies back up this simple fact.

The problem that registry cleaners can create, however, is when they are too aggressive in cleaning out your registry. And since there is so much competition in this category of software utility, the software makers promise better results by being more aggressive. They improperly delete keys and values, so that when a software program goes looking for the information, it is no longer there.

I'm going to echo arraknid again:

"The best advice is NOT to run ANY registry cleaner, any time, anywhere!!"

And other Windows experts agree: Ed Bott, Leo Notenboom.