As a newbie I was advised to buy a full season ticket so I could try anything.
This was very good advice and I would offer it in turn but I have never bought one since. Partly because I go for such as are in Leadfingers 30th June list plus absolutely the Middle Bar singers in the Anchor ie non ticket events.
Partly because however good a show might be (see Ruth Archer 30th June list) I won't spend half my day queuing to get in which you may well have to do even though you have a ticket and you might still not get in!   
(Plus I struggle with the heat. Last time I had a Ham marquee ticket I came out and listened outside.)