If you plan a cachingtrip and what to log interesting caches it is useful to add the caches to the vgps. For example High FP, %FP, uncommon types, interesting DT, solved myst, old caches, caces needed for some challenge, Easy stop in a new county etc
You have a nice overview of what caches you like to log and can create a GPX to have a separate list of those caches on some cachingapps.
It can also be used used to replace PQ:s to download caches you have more options in choosing what caches you what to bring with you.
The video below describes how to use pgc to plan a trip