Beta reading has helped remind me that people react differently to every situation. Just because I would assume one thing doesn't mean another person would react in a different way and that's good. All my characters have different backgrounds and should see situations in different lights.
2) Admiring another writer's strengths- I know there are things I'm not great at. We all have flaws when we write and sometimes seeing how someone else handles things we are bad is a great learning experience. I'm not saying to outright copy what that writer is doing but it is interesting to break down how they handle a situation that you are bad at.
3) Allowing your mind to think about other plots and characters- I find myself daydreaming about this book I'm reading like I would my own work. I think about how I would write certain scenes and where I would take the novel. I play the guessing game and see if I'm correct in figuring out where the plot is going. This gets my mind active and I find that when I return to my own characters and stories, they are richer for it.
4) Having fun- This kind of goes hand and hand with the last one but I find that I have a lot fun beta reading. I think it is because I get an inside look at how a story takes shape and sometimes I can help make it better. It doesn't hurt that I don't have to do all the work that comes after. =P
Do have you beta read for someone or are you thinking about it? I haven't done it too much because I'm such a slow reader but I think I need to start doing it more, I'm really enjoying it and I'm learning a lot along the way.
What are some of the things you learn when you beta?