Let's say I want to verify if some PPAs aren't being used so I can minimize conflicts or whatever else could happen. Is it possible to verify which PPAs are no longer in use?
One method is to use Ubuntu Software Center. Open it and use the arrow down next to "installed". It will list (from bottom up) PPA's installed:
When you click on a PPA (TLP as an example) it will list the software included in this PPA. A green 'tick' means the software is installed. If none are the PPA is unused.