If you're third in the FP line then no. But you can't (at least couldn't to that point) get a FP for every ride. So you need to balance your 10 minute wait on Splash (while you're cutting in front of 300 people) with your 50 minute wait on Thunder (while 300 cut in front of you). I think most would be okay with an average 30 minute wait spread out between both rides.
FP isn't intended for one ride. It's designed based on averages. If you want to go into a park and ride 3 rides and leave - then that's your prerogative. But there are many others that jockey for additional FP and even wait in regular lines.
Your day isn't broken up by windows. If though, you can get 10, maybe 12 rides and wait an average of 20-30 per ride, have time for a TS or quality QS, watch a parade, and do some shopping........who cares "who cut in front of you".
Which is why it’s illusory. Best case scenario, your wait is simply shifted. You save 30 minutes on 1 ride, but wait an extra 10 minutes each on the next 3 rides. So your average is unchanged — and that’s the best case scenario.
If FPs have no impact on wait standby lines, why not just give every dingle guest unlimited FPs? Ahh… Because the more FPs you give, the more it affects wait times.