Registry Cleaning in XP

I Ran a registry training program today; it's owned 156 invalid items and removed them. I ran just a normal scan. Then, in the help menu, I read this:

Basic usage

To clean up your computer's registry, simply start the program, click the Start button to start the registry scan. Wait while it works and and after that select all items and click the Fix button from the lower right corner of the window. The program automatically creates backup from all data it modifies or removes.

Warning

Using the registry cleaner of RegSupreme can damage your computer, in such case you might even have to reinstall your operating system. This kind of situation is rather theoretical but still possible, if you do not know how to recover your computer from such state you should not use any registry cleaning program.

Using the Aggressive scan option also clears all detected MRU (most recently used) data, such as last opened lists of Microsoft Office, for example. If you don't wish these items to be removed don't use the Aggressive mode.
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But I don't know if I want these items to be removed or not. I mean, how does one know--how does one decide?