Getting punctuation right shows that you are a careful writer who cares about detail. Getting it obviously wrong makes you seem sloppy or rushed. This can have the effect of mildly irritating the reader to complete misunderstanding of parts of your text.
Do you know the differences between:
- Its and it’s?
- A colon and a semi-colon?
- Commas here: The painting, which I bought last week, is perfect for my new house.
But not here: I’m going to put the painting that I bought last week in my new house.