yes, for a formal presentation that doesn't get to have a response to say 'what do you mean', Grammar does matter.
In an interaction when you are conversing in close contact an over attention to other people's grammar is a dominance ritual of those who need, desparately need, to have an 'edge', when the edge simply doesn't exist, no matter what someone says you think that they mean.
Grammar Nazi is a bad thing to be
Grammar Nasty is a bad thing to be
if you don't understand
then you can always ask me . . .
the point of 'good grammar' is that one is not available to be asked.
however, if you are interacting with someone is a close situation, harping on their 'grammar' is a dominance behavior, and shows you to be a bit of a control freak who wishes to rule, even when you dn't have the better ideas.