Wow, this thread is old!
I see no reason to play the Grob over a more solid Benko's opening (1. g3). It doesn't do anything that 1. g3 does not, other than setting up a naive pawn march on the king side, easily refuted by strong counterplay at the center, while at the same time forcing white to spend time attending the defense of that ugly pawn, weakening the black squares irreparably and, overall, not doing anything useful. After
White doesn't have a good continuation and has to resort to passive defense to even have a chance at surviving this.
Grob probably could work in blitz/bullet games, where white can launch a caveman attack on the king side and black doesn't have enough time to come up with proper refuting moves - but in standard games, let alone in daily/correspondence games, the Grob might as well be called "Seppuku opening".

Yeah not only that, it peeves people off, as they have to spend evening playing someone elses stuff, and often being in that negative space they do not play at their best
I think that's actually it, you nailed it. You're sitting there, you've worked on all your openings, and you're pretty ready for anything, and they throw this crap on the board and you couldn't have been ready for it. You can't study everything, so you had to spend time on the important stuff. And what's more, what's really annoying, is that you know the opening is crap, but you know they've sat at their computer for probably weeks coming up with all the damned responses with Stockfish and you know, damned good and well, you're about to have a very difficult game, or lose, to this stupid opening. And they KNOW you think it's stupid, and they are counting on that very thing. It does kinda piss ya off really.