It's grammar that matters, not tools that pick up a handful of borderline grammar issues and false positives over and over again, while missing many more important problems. I'm pretty good at spelling, but spell checkers still catch me out several times a day. I'm only okay at grammar, but I can't remember a single instance where Microsoft's tool has been helpful.
the recipient is aware that the sender gave him more work to do than was necessary -- something usually not considered a compliment.
Yes, the recipient will be aware that you don't value their time enough to spend some of your own crafting a message that's straightforward to parse. It's worse than that though; particularly in electronic communications where you're often fighting for a limited slot of someone's attention, you've just made someone spend a bunch of time deciphering your meaning, reducing the amount of time they've got for actually considering your meaning.
Making a message easy to parse doesn't necessarily mean formal grammar - there are all kinds of short-cuts you can take and still be unambiguous, particularly when you know your audience well. In most business settings you probably want to avoid that kind of short-cut though, so it's worthwhile learning formal grammar if you ever want a job that requires a written application.
Does it matter if you use bad grammar in some settings? No. Does it matter if you are incapable of using good grammar? Yes, I think it does.
Machines have less problems. I'd like to be a machine. -- Andy Warhol
