Drag force of a reel is the amount of power with which the reel can retrieve a fish once it has taken your bait. Baitcasting reels usually come equipped with enough drag force.
However, if you are content angling for small fishes, then reels with low drag force will prove sufficient. On the other hand, if you are looking to catch big game fishes, then reels with a higher drag force will be required to bait them.