To put it simply, Uninstaller compares the state of your system before and after the installation of some package to keep a record of things that were added (not changed) to your system. Later on you can select the record and choose to view/delete it or go for an automatic uninstallation following the record. The automatic uninstallation will erase everything that you havn't deselected from the record. (For example, if the record shows 'MSVCRT.DLL' with other files, and you do not want to remove it, then you can unheck this file to keep it from being removed automatically.)
