Adobe Reader and Acrobat Cleaner Tool fully removes a standalone installation (not a Creative Suite or other Adobe suite install) of Reader or Acrobat. It deletes all program-related files and Registry keys, including settings and preferences which might otherwise by preserved after a regular uninstall.
Why bother? You could use it just to try and remove a little more PC clutter, but that's not recommended; it's always best to use your program's own uninstaller first. Adobe Reader and Acrobat Cleaner Tool is aimed at emergency use, perhaps when you can't uninstall or upgrade Adobe Reader or Acrobat via the normal routes, and want to fully remove the program so you can start again.
Whatever you want to remove, Adobe Reader and Acrobat Cleaner Tool makes it fairly easy. It's a simple wizard, so all you have to do is choose the program you'd like to uninstall and it'll be removed for you. A log fills you in with the precise details, if you need them.
Adobe warns that there is one particular issue that might crop us as a result of using the Cleaner Tool: "If you have both Acrobat and Reader installed, removing the product that is the default PDF viewer can result in the other product failing to become the new default PDF viewer. When this problem occurs, run Repair on the remaining product and reboot the machine to make the remaining product the default PDF handler."
This isn't a tool you'll need to use often (hopefully), but if you do have problems with an Adobe Acrobat or Reader install then it's worth knowing it exists