My son had stereotactic radiation after 3rd resection, but I don't think it did any good in his case. I don't think it did any harm, either. He didn't have any side effects except a little more hair loss where the hair was already very thin from radiation in the past. (It was hard to tell if it left him more tired, as he had just had a third resection, and surgeries # 2 and 3 were just two months apart.) I believe that studies show that it can help, and that the brain can tolerate more radiation than what is considered to be maximum dose. I know that there are concerns for long-term effects.
I looked at various articles/studies before my son had his and felt comfortable that it was the right decision. If you do web search for "stereotactic radiation recurrent glioma" you will find some studies and articles.
I was also comfortable trusting his doctors' recommendations, and we were looking for continuing treatment options with less toxicity. The hope was to knock it out and buy him some more time, but he had more progression a couple months later.