Clock management in football is incredibly important - the last 17 seconds can take multiple minutes to play if the team has timeouts, throws out of bounds, all sorts of things.

You want to burn the clock if you have the ball and 17 seconds remaining, because you don't want the other team to have a chance to retaliate.

It's a very delicate balance and one of the most difficult "coach" decisions football has, and it applies throughout the game, and changes based on how your offense and defense are doing vs theirs (do you score fast and hope to defend and score again, or do you score slow and hope to defend only, etc).

Now the opposing team gets less time to score and possibly win.