You don't need to offer chick grit if they are only eating starter feed. But if you give them any treats then they need it. I just mixed some into their feed when I started giving them some dried mealie worms at 1-2 weeks old.
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The above from sunflour is accurate.
However, providing grit to chicks will help develop the gizzard and can still aid in grinding feed that has already been ground at the manufacturer.
I never used to offer grit because I only fed starter feed. Then one day I decided to add another feeder with just chick grit in a pen of about 10 chicks. In very short order, they consumed a half quart of chick (#1 grit).
If you offer grit, it should be lightly sprinkled on top of the feed the first couple days, then offered in a separate container.