Yeah, if you are staying in the same park you have to use, burn or otherwise let expire, all 3.
It's only for hopping that things get complicated. It's something I didn't quite grasp till about 6 months ago. The trick/key is not booking all 3 in park 1. You don't really want to book all 3 in park 1 as it just delays you getting a FP in park 2. Unless you want 3 in park 1. Then by all means book 3. This is only a technique to use when you don't want 3 in park 1.
Say you book Soarin' at Epcot at 60 days, nothing more. You plan to go to HS after riding TT stand by and Soarin' with a FP. As soon as you tap in to Soarin' pull up the
MDE app and start to look for FP at HS.
You can book a Tier 1 at HS, and a Tier 2. You can do this before you even get on Soarin', since we know there is almost always a wait in the morning.
They don't have to be Tier 1 FP but since they are the most desired in most cases that's what most folks use this technique for