Oh yeah, it's definitely a preference thing, but that's why I thought it was interesting you were telling someone to stop doing it. I have found it has some pros and cons, same with full grip.
I actually prefer having a beginner use a thumbless grip from the start, if that's how they like to bench, mainly because I figure it's better to figure it out then versus building up to a 400lb bench and THEN trying to change things around. Sorts out the learning curve.
Every dropped bench I've ever seen was done with a full grip. Meanwhile, you got strongman competitors false gripping axles over their skulls who aren't dying, haha. I guess I just don't really believe in the danger aspect people talk about.