It's interesting to see that the answers are as unique as everyone's children. We've always had Hoppers, back to when our oldest was an infant. Now he's 5 and his little sister is 3, and we still couldn't imagine a trip without having that flexibility.
We normally start the day in one park (for instance MK on a party night), go back to the room/pool for a little quiet time mid-afternoon, then head back out for dinner and some evening fun in another park. Sometimes, the second park is what we planned, sometimes it's based on where we eat, and sometimes its just because.
I can't use the word "flexibility" enough. First, we can plan meals around what we want to eat and what reservations are available (even at 180+10), instead of having to plan around park days. Also, we've had days where we've gone to a park and it's been shoulder-to-shoulder, can barely move crowded. This happened to us last November in AK. Having Hoppers, we were able to bounce over to MK and use the
MDE app to schedule an endless progression of FastPasses in a much less crowded atmosphere.
Te each his/her own. I'd never call out anyone on the way they prefer to travel or see the parks, but for us, Park Hoppers have been the difference between relaxation and frustration when plans went sideways.