Don't be a stupid fool, you know that spelling and grammar are important but clearly not as much as the substance of your work. You can't get perfect mark without work. But it every one start to use this kind of tools and the average people start to becoe near perfect in spelling and grammar without effort in order to get an easy advantage, then in this case yes! Teaches will start to slowly expect perfection by default.
Do you want that? I won't because it's not the aim of this exercise.

If your problem is small grammar mistakes it's likely that Grammarly can help your grades. It helped me keep my grades up throughout high school.