I understand a lot of climbers don't like using gri gris for sport and trad. I was wondering if there was a reason, and if it was valid.

I use my gri-gri for belaying on multi-pitch routes when on lead. When I reach the belay station I set an anchor, pull up the rope and then use it to take in slack from the climber below. I like the added security of having the locking device when I'm responsible for someone else making it to the top.

I dont know about that but where i live you dont go outdoor climbing without a gri gri. People tend to get distracted and sorts but if someone suddenly falls and your not paying attention its gonna catch. I asked to belay with atc once and everyone just stared at me. I recommend gri gri its very safe.

I use a grigri primarily for sport belaying for the same advantages you get when top-rope belaying: If the climber is going to spend large amounts of time hanging on the rope, it makes the belayers job SO MUCH easier. I usually don't use a grigri when belaying trad because the device will lock up immediately in the event of a fall, creating a less dynamic belay (dynamic belays are a good thing, especially when climbing trad when gear may be suspect). I'll usually use a ATC when belaying trad. The grigri is a excellent piece of equipment and wonderful tool when used properly.