The FP line has a different and much shorter path through the garden area and if the crowds are low will skip the garden entirely.
Both the FP and standby line then enter the (Lobby I guess?) with all of the creatures and artifacts in cases, but the FP line then immediately enters the pre-show staging area, whereas the standby line loops through the room giving you a closer view before entering the pre-show. From there it's all the same.
As others have said, it's very easy to exit through to the gift shop if you don't want to ride. My son and I love it, but my daughter and wife both refuse, so they will often enjoy the queue with us and then step out, just make sure to tell the cast member loading the gantry lift so they can fill in the extra spots.