1 & 2. Yes I have used it, last summer. I figured someone would throw out the "you don't have to plan that far, there are plenty of FP+ the day of blah blah blah." No there isn't. We planned 30 days out last year and guess what, couldn't get 2 of the 3 things we wanted. And guess what else, nothing available checking back the day of, the day before, the day before that.................. So you are right, I don't have to book in advance. But we want to take the advantage of the HUGE cost that is Disney, you bet you have to plan well before your time comes up.
3. Its not about showing up and "winging it". I doubt if you asked people they really want to plan what and when for their rides that far out. They do it because they feel they have to. Again this may be in your wheelhouse but not mine. We never wing it, but we also never needed to plan things out this much. So what if we need/want to change what park we are going to the day before? Well there goes getting a pass for soarin, or toy story, space mountain...... So we have lost flexibility.
4. Yea, awesome, no more running across the park for a fastpass. Oh wait let me stand in line for 20 min or more each time for my additional passes for stuff I have never needed a fastpass for before. After our 3 passes were done, they had no passes for any major attraction.