So, extra magic hours are supposed to be great for getting in rides with less crowds, right? So why do I see some people mention avoiding parks that have EMH? Does the whole thing sort of backfire and parks with EMH get OVERcrowded? Wouldn't that defeat the purpose?
It's actually pretty simple --- By advertising EMH, a disproportionate number of resorts guests end up at that park.
Whether you can get value out of EMH depends on a lot of factors:
Morning EMH can indeed be a great less crowded time. Just like rope drop is a great less crowded time. It's the benefit of waking up extra early. So IF you are really capable of getting up that early, and getting to the park before morning EMH rope drop, then you can get great value out of the morning EMH.
But if realistically.. you are going to get to the park around 8:30-8:45... only getting in 15-30 minutes of the EMH... By 9:00am, you have the EMH herd PLUS the regular rope drop herd... So by 9:00 am, the park is MORE crowded than it would be on a similar non-EMH day.
Evening EMH has the opposite effect. Let's say the park closes at 10pm, but there is EMH from 10-1am. So the entire afternoon/evening, you have the regular non-resort crowd PLUS extra high number of resort guests who are there because of the upcoming EMH. So for the afternoon/evening, the park is MORE crowded than it would be on a similar non-EMH day. And as resorts guests tend to be more likely to stay up late rather than wake up early, the beginning of the evening EMH can be nearly as crowded as regular park time, with less rides actually operating. But as those evening EMH hours get later... the park does empty out. So by midnight, it can be a great experience, IF you are up and active at midnight.
So it's not that EMH hours are bad. They are great IF you really use them.. if you really can get there super early in the morning, or can stay at the park super late at night. The issue is, during the non-EMH hours, the park is more crowded than it would be on a non-EMH day. So if you aren't parkhopping, you may find that good extra couple of hours, not worth having a much worse regular hours.