We used it on our trip to WDW 2 years ago and it was definitely worth it.
We were in the parks 7 full days. We stopped as often as we could to the photogs. I have great pics of our entire family all over the parks. Yes they are out at night and one of my favorite pics is at night in front of the castle.
The photogs are also at the waterparks. We never take our camera to the wp so it's nice to have some pics.
We made an effort to use the photopass everywhere. We took a lot of pics with characters as well. Now last year, we were only in the parks 3 days and we didn't use photopass and don't regret it. However I don't have as many great family shots.