On my summer Constellation cruise, we went to the late afternoon time and no one else showed up. We didn't stay long.
I do like being able to wait in a smaller, quieter place for the call to disembark. I've done it twice now and there's hardly anyone else there. There was coffee, juice and pastries, eliminating the need to rush anywhere for breakfast.. Beats being squished into a nightclub, sometimes with nowhere to sit.
I also like the coupons for 20 pieces of free laundry and 90 fee mins. on the internet. There is an extra cocktail party and exclusive tours of the bridge, galley, and backstage. There are other coupons having to do with bingo and the casino, which I don't use.