It seems it's a fairly cookie cutter program that wastes an awful lot of bytes and CPU cycles on just emptying your recycle bin, removing "internet clutter," (i.e. clearing your cache and temp files), removing broken shortcuts, twiddling your run-on-startup apps, etc., which are all actions that are not only fabulously unlikely to make your Windows machine perform any faster but are also all things you could do yourself in about thirty seconds.

I lifted that screenshot from this video, chosen purely on the merits of this guy's hat.

You can also find plenty of places to download the installer found on the Win Cleaner USB drive (it's just a cheap USB storage stick in a funny shaped housing) and try it yourself... possibly preferably inside a virtual machine.