I think the "wait until you get there" idea is not a good one. If you have hoppers in advance you can make all your plans in advance.
We quite often start our day at one park without FP+ (morning EMH maybe), when it gets crowded mid-day we hop to our FP+ park. We usually try to get fastpasses beginning at 11:00 giving us 3 hours at the first park. We have now gotten to experience 6 or more attractions with little or no wait times possibly before 1:30.
We can also check for extra fastpasses and if we find something we like a quick 20 minute or less ride (via express bus) gets us to another park. The VIP buses are also a nice, scheduled, 20 minute air conditioned break usually i a bus with less than 20 people.
This also allows us to get ADR's wherever we want (within parks or not) as we are not tied to a single park all day. Our day often starts at one park, FP+ at a second park, and dinner at Epcot for example. All planned well in advance.
It makes a lot of sense to us to do morning EMH knowing that park is going to get really crowded mid-day (historically), then hop to another park.
I wonder if those suggesting the lost time between parks as a reason for not hopping have actually used the express bus option. Inside one park to inside another in 20 minutes or less is no different than being in a standby line for 20 minutes (other than the actual attraction itself).