It’s hard to go through a day without encountering directions of some kind, and commas often play a crucial role in how you interpret instructions. See how important the comma is in the following directions for making hot cereal:
Add Cream of Wheat slowly, stirring constantly.
That sentence tells the cook to add the cereal slowly. If the comma came before the word slowly, however, the cook might add all of the cereal at once and stir slowly.