FoLK does not generally need, nor do guests benefit from having, a FP+.
(We always, always, sit in the warthog section and have never used a FoLK FP.)
However, there IS a definite positive for using a Finding Nemo the Musical FP+.
Arrive at least 30 min. before the Nemo show for which you have a FP+.
(They will let FP guests into a line to wait for the end of the show that's going on inside.)
At about 12-15 min. before show-time (which is just after the previous show's guests have exited,) they will open the theater doors only to the waiting FP guests and they can enter and choose from any of the prime seating that they choose.
After the FP guests have chosen seats, they open the doors to non-FP guests who can
find any still-available seats.