My degree is in creative writing, which means I've done a whole bunch of the "writing group" thing, and that's kind of soured me to it, TBH. It's good to use as an excuse to churn out new work (although IME a lot of people recycle the same story over and over again, which is kind of annoying) and it's interesting sometimes to see your own errors in other peoples' work, but... I guess my biggest issue is, if you're not being critical enough of your own writing you're not likely to be accepting of other peoples' criticism, and on the flip side if you *are* critical enough, having other people give you advice is frankly of limited use most of the time. Sometimes it does help to have someone who knows what they're doing read through your stuff just to let you know if you're completely full of crap or not, but you don't need a writer's group to do that.
I do have to say that if all you get out of writers' groups are simple proof-reading and spell-checking, you're doing it wrong. REALLY wrong.