2, you know how staggling humans like to run past you and you can't time your swing? this fixes this, hold down the left click, and as soon as in thier in range they get infected.
3. it's great for when you're oin a crowd of humans, and you can't swing fast enough? now you can!
there's three reasons why it's useful, and since you failed to see how it would help, you must be both blind and mentally retarded.