It’s harmless is almost all lines. The one where it’s actually a serious line is the Taimanov. Black is fine, but at least it’s a decent try for an edge. It’s also played against the Najdorf and Dragon on occasion, and while there isn’t anything wrong with that neither is particularly worrying for Black in comparison to main lines. I figure g3 wouldn’t be too bad against the Scheveningen but then why not play the best move which is moving the g pawn one step further. I’ve seen it played later on in some Sveshnikov lines but I’m assuming you mean White playing g3 on move 6. Here’s the aforementioned Taimanov line
when is the open sicilian with g3 effective and when is it harmless theoretically