I had a job to fly indoors recently, so I put on the prop gaurds. It gave me a sense of protection. But eventually, flying indoors in this gym, the heating ducts airflow caught the solo and it drifted into a wall. A minor crash. Normally, a crash like that would have shatteded a couple of props. Upon inspection , I found that indeed one prop did get a nasty chip in it. So, the gaurds saved 75% of the props. Was it worth it? I guess so, but I rarely use them.
When I know that I need to fly in close proximity to people, I will put them on. I would rather have a bit of insurance, and take the hit on performance.