Well generally, cracking your knuckles threateningly makes it easier to hit someone, in fact, it's the only reason I can think of for cracking your knuckles.

And you can't punch through the internet

Really? Cracking your knuckles makes it easier to hit someone? Want to try that again?

It hurts more if you hit someone and that makes your knuckles crack. If you crack them before hand, there is less pressure applied, and less pain on your part.