I've been to a couple events here and this place is perfect for holding big events. All you have to do is brink a chair, or blanket, snacks, and drinks(if permitted) and you're set for a good evening. During the day you can find a nice spot under the shade and as the day goes on, more shade becomes available. Anywhere you set up here is a great spot to see what's happening on stage. My family and I went to a festival here and when it was over, we went over the outlet mall, which is across the street. In the same area is the Smith Center which is beautiful after dark, also in the day.
There are many things to do in the area and you could plan a decent day/evening; relaxing on the lawn in the amphitheater is one of them.