Many programs, like Office, stores several registries about the installation process in different places. This information isn't of any use if we check that the installation has been accomplished properly, and all the files and processes are working as they should. For theses cases, Windows Installer CleanUp Utility is perfect, because it deletes all these registries.
Thus, if we think that an installation has finished properly, we can use Windows Installer CleanUp Utility to clean the Windows Installer and thus manage to make sure that it always works properly. Small utilities like this make Windows resist the pass of time a lot more.