Accurate grammar and punctuation makes life easier for your reader. Making sure that your sentences are strong and accurate means that you're conveying the information concisely and effectively.
Inaccurate punctuation and sentence structure can lead to confusion, misunderstandings, and, in some situations, serious safety risks.
Here's a funny example:
Let's eat Grandpa!
(I bet he'd taste delicious!)
Let's eat, Grandpa!
(I'm hungry. Let's eat!)
The meaning of the two sentences above is dramatically different. In this example, the comma in the second sentence saves Grandpa's life!