A couple of points to consider for AP holders.
First, FP+ might be subject to the same limitations as ADRs. If you don't book 180 days out, the "good" ADRs tend to be gone. Similarly, it might be that if you don't book your FP+ experiences 60 days out, you could be out-of-luck getting the "good" FP+. Still, we don't know exactly how FP+ will work so this is just speculation.
Second, Disney's Terms & Conditions page indicates it will be possible to change or even cancel FP+ experiences. Depending on how it works, I can imagine AP holders keeping a "rolling" series of FP+ reservations. For example, let's assume an AP holder only visits on weekends, they could, for example, make reservations 60 days out for Saturday & Sunday, hold onto those and, one week later, make reservations for the next Saturday & Sunday, etc., until they use up their allotment. Then, simply cancel upcoming FP+ once they are sure that they won't go on specific dates. The idea is to make sure the entire allotment of FP+ reservations are being "used", and then cancelling these, as needed, the day before for days that won't be used. I know I'm not explaining it well but, in a nutshell, have a running set of FP+ reservations for the days you think you are most likely going to visit WDW.