I used LLPP for the first time last week - Sunday in Epcot and Friday in MK (bookending a Wish sailing). It was certainly convenient to not have to worry about return times selling out or conflicting with other plans - and since Friday was our debarkation day, it allowed us to do a lot in a relatively short amount of time. We were celebrating a family member's graduation, so this fit the "special occasion" rule my wife and I enacted when LLPP was announced. With the cruise eating into our park time, it worked out well for us.
We didn't arrive at MK until after 11 AM and still hit everything we wanted to. We started in Adventureland and worked our way around and did Jungle Cruise, Pirates, TBA, lunch break for some of us while the teens rode Tron and Space Mountain), Buzz, MILF, 7DMT, Pooh, Peter Pan, Small World, and Haunted Mansion all before 6 PM. After that we had dinner at Be Our Guest and decided to skip the last few remaining rides because thunder storms were moving in and we decided to not chance getting soaked. By my count tracking our waits vs the posted wait times, we saved 267 minutes (closer to 350 minutes for those who rode Tron and SM while us creaky-backed people ate lunch). I know posted wait times are often overstated, but at least 7DMT and HM had lines that looked much longer than their posted waits based on my previous experience (and we had experienced multiple standby wait times earlier in the trip at DAK that were longer than posted).
In Epcot the previous Sunday, my estimated time savings was 220 minutes total for Spaceship Earth, GotG, Mission: Space, Soarin', Frozen, and Remy leaving us plenty of time for all of the festival food booths, topiary displays, and photos we wanted. Frozen went down at least twice that day and we managed to squeeze it in between those issues, so I'm not sure how much that impacted the wait time's accuracy.
Overall, it was worth it for this trip - the prices weren't near their max and this was a special occasion for our group. It's definitely not something I would make a habit of doing as someone who visits multiple times per year, but it definitely made the trip better. Had we been staying at WDW all week instead of just before and after a cruise, we likely wouldn't have bought LLPP since we would have had EEH at both parks. We probably would have just added park hoppers to the tickets for the non-passholders in our party and added 2-3 days to the tickets with LLMP for DHS (skipped this time to avoid the May the Fourth crowds).