Exactly.
For our upcoming trip over Christmas, I’ve deliberately “over booked” MK. On at least 1 and probably 2 of those days we’ll switch to either Epcot or AK. Neither are likely to sell out.
Exactly which days those turn out to be might be decided ahead of time (depending on dining, for example), or maybe we’ll decide just the night before. But meanwhile I’m blocking others from being able to book what they want.
But that’s what the park reservation system encourages me to do.
The only thing is, MK is usually the park with the most PM hours, unless you are going prior to Dec 22.
I can understand booking MK more now, but when we were actually at WDW, on days we bought G+ at least, hopping TO MK at 2pm or later worked well to get the most out of G+. It depends a little how you tour, and how late you stay out, and which attractions you want.
It was especially helpful on rainy night to hop TO MK. On our HS, by mid-day, there was nothing left to G+ as HS. We did MMRR during EE, then TSM standby (15min). We got a G+ Slinky, skipped MFSR (been on it before, for us, meh.). We did G+ for ToT. On our most recent visit, I think SR was down for RNRC one of the days, so we used G+. We were also able to get a now-time pass for Aliens one of the times we were walking right past it. Maybe can't do that Christmas week though. After that, we didn't need G+ for attractions like Muppets.
So we were pretty much done booking G+ by mid-day, even though we stayed a few hours past that. that's when we started booking MK G+.
We did well with the :17 and :47 after the hour drops. I was able to get BTMRR, Space, and Splash all overlapping at 6pm to (window end) 7:15pm time window....but....it started to rain just as we were getting to Space Mtn. So when we got out of Space, rain was coming in buckets, and YOWZA! There was some fierce lightning. Our other passes all converted to any time passes, but much of the park was down due to weather for most of the night. Very late, we were able to get on Splash, but BTMRR never reopened.
What we were able to do though was to hop from one G+ to another. More or less. After Space, we got a G+ for Buzz. when we finished Buzz the weather was scary, so we only went as far as CoP. But after CoP, we got G+ one right after the next for most of Fantasyland. At the time we went on it, LM was 45min wait, but we walked right on it. I think few people in MK had G+. At the end of the night, we still had one anytime pass left over! I was hoping to use it on BTMRR.
This is the key: with G+ you can only do each attraction once. Come 11am in HS, our G+ options were down to almost no options, but over in MK every G+ attraction was a possibility. The other lesson was the very big impact storms have on G+. Much of MK was down. If had been in MK all day, we would not have had as many G+ options to choose.