We are early risers, so we always take advantage of early EMH at MK. We rarely use the early EMH at EP as there isn't enough open to spread the crowd. If AK and HS early EMH fits into our plan, then we will use it. For both of these parks, if you stay away from the crowd draws of FoP and TSL, then you have the rest of the early EMH attractions almost to yourself. If you can't get a FP+ for those popular attractions, then early EMH is a smaller crowd than regular opening to navigate through, but you still need to be at the gates 30-45 min before the EMH opening, so that makes for a VERY early morning.
Late EMH is too much of a crap shoot for us to make it a firm part of our plans. Right now, the only two parks that even have a late EMH are EP and MK. EP doesn't stay open late enough for the crowds to die down and again, not enough attractions to spread out the crowd. We would make time for a late EMH at MK if the last hour of EMH is at least 11-midnight or later. Otherwise, it's not late enough and there are just as many people there as during the day.