What does the Repair tool do in Programs and Features?

Question

I've noticed that some of the issues our users have within a third-party application, Microsoft Office 2010 for example, can often be resolved by running the Repair tool within Programs and Features. Does anyone know what this tool does exactly?

Solution

Some installers, (like Windows installer) have this option.

The repair option either runs the backed up installer (backed up at installation by the installer itself) or asks for the installer if it's not present. The installer then compares the local installation with its manifest and replaces missing or corrupt files/registry keys/dll registrations.