Amen....never could understand it either. I have showed up early (9:30-ish) because my flight came in early to the embarkation port. It's a mass of people who just disembarked from the previous cruise along with those who are trying to embark on the current cruise. We were all wandering around for at least an hour, maybe an hour and a half, just milling around the checkin area. In the Haven, while I appreciate the lemon water, coffee and cookies, it's still not worth "hanging around" getting there that early.
If you're not in the Haven, you're vying for a seat in the waiting area. HINT....it's not comfortable and IT IS crowded.
I'm a 12:30-1:30 person. I get there at that time, miss the big crowd, usually check right in and then board the ship immediately.