We chose the second showing of ROL as one of the FastPasses two weeks ago. We were crammed into one of the middle sections, which is prime seating. They sure squeezed everyone into that area. But the two left and two right sections were wide open for anyone to walk in and sit down.
In retrospect, I wish I had not tied up one of my FP selections with ROL. The show is okay, but I could've scheduled my FP earlier in the day and sacrificed the center view for the chance at more rides.
Disclaimer: this was in June 2017, and the parks didn't seem all that crowded this June. Maybe FP are essential if you want the first showing or during a busier time of year.