As a tool I think it and other programs are great (like I said, I suck at grammar) but I find, sometimes, when I'm reading the writing takes on a "robotic" type feeling, like @steffiemusings said.
That's where I think people might be in a hurry and a suggested line comes up and "that'll do."
"That'll do" always reminds me of my father who used to say "good enough... isn't"
But, it's up to the writers and I think, from what's being said on this thread, most are using the "tool" aspect in helping with grammar, spelling and punctuation and applying their creativity in ways that might make Grammarly and other tools like it be the new game of not turning left and hearing the words "recalculating."