That depends. Are you going in early June or mid/late June? If it's early June, you'll probably want to take advantage of them; but once it hits June 10 and onwards, EMH days are total zoos! If you're park hopping, taking advantage of the early openings would probably be okay, as long as you hop to a different park afterwards. But the EMH evenings? I went in the middle of June on EMH days this past year, and I will NEVER do that again. Two hour waits for most of the rides, fastpasses for six hours later... People were packed in like sardines (or pickles) everywhere. That, combined with the heat/humidity, can make it less than an enjoyable experience - and that's BEFORE the EMHs even went into effect! It seemed to only get more crowded after dark.
But that's just my $.02.