I think hopping can be a flexible option for families who aren't quite sure what they'll expect at Disney. We went seven days and ended up hopping on three of them. One wasn't planned. We split a day at Animal Kingdom then hopped to Epcot after supper. We had FastPasses for Epcot that evening so we were able to get FastPasses for both Frozen and Test Track on the full day.
The flip side was that by lunch on our full day at Epcot, we were getting bored with Epcot. By mid afternoon, we gave up midway through the pavillions and just headed back to our hotel for some pool time. Basically, we trashed our Touring Plan for the day. After supper, we hopped back to Magic Kingdom and had a blast.
The next day, we had a full day planned for Magic Kingdom, then suddenly Rivers of Light opened up...but not on our AK day. So we ended up leaving MK early and going back to AK for a dining package at Tusker House. The show was better than the food.
Did we need to park hop? We could have gotten away with not doing it, but I think we ended up having a better time by hopping because we were able to see some attractions that frankly wouldn't have fit into our plans. And we had the freedom to hit the eject button on Epcot in favor of doing something our family enjoyed much more. I recognize how inefficient it was with our time, but it was nice having the freedom to adapt our plans on the fly.