Grammar helps the mind think, and a person's mind is his privacy, a very delicate part of him. So feeding this part of him with a rushed jumble--forgetting grammar---hurts the mind---and is harsh to it. Few people spend time hurting. So write, and write well.
Yet, in saying all this, there are still audiences for whom grammar may not be necessary, because it may not lead to understanding, and understanding should be the chief reason for writing. But then again, for most literate audiences grammar is crucial to helping the mind properly process what the writing is about.
Ever heard this saying by B.J Chute: "Grammar is to a writer what anatomy is to a sculptor and the scales to a musician, you may loathe it, it may bore you, but nothing will replace it, and once mastered, it will support you like a rock."
Alright, off to your slate. Write.