I don't think that "sitting on FPs" is much of an issue. I assume that the rate of unused FP is relatively constant and that they can easily account for it in the available inventory. For an AP, especially a local, sometimes you plan to go to the park and something happens last minute. There shouldn't be a penalty for this.
A couple of days ago I booked FPs at MK in the afternoon. The plan was to go to AK in the morning, ride FoP on standby, then grab some lunch and head to MK. Well, after waiting in line for FoP for almost 2 hrs, they had the building evac. Then I waited on line for another 45 minutes at guest relations and was given a FP to return later if it opened.
Since I figured it would reopen in a few hours, we decided to have lunch and go see a movie at Disney Springs. When the movie ended, FoP was back up and running so we went back to AK to ride it. We had other evening plans so I didn't reschedule the MK FPs. Other than Pandora, there weren't really any waits at AK so there was no reason to try and book FPs at AK.
I didn't cancel the FPs just in case we decided to try and go to MK for a while after AK. By the time we made the decision not to, we were already 1/2 way into the window for the second pass. I didn't really think it was worth the effort to cancel the last pass so that somebody might get to book something 1/2 hour before the slot.
I wasn't "sitting on" the passes but there were events that changed my plans last minute and I ended up wasting them. Any other times in the past where I've not used FPs were similar. I would have every intention of going and then something would come up. I don't think I (or an other AP) should be punished for trying to use my AP in a somewhat spontaneous fashion. Under the old paper system, this wasn't an issue. With FP+, if there is any likelihood of going to the parks on a particular day, I need to reserve FP+.
If there was a punishment for "wasting" FPs, they would have to also do something like reserve a certain number of FP slots only for APs that can only be booked day of or something like that. With FP+, you can't enjoy a day without having the 3 FP bookings set up in advance.