Cracking your knuckles releases fluid buildup and pressure which helps your fingers and hands feel much better afterwards.
Some people have said that cracking your knuckles leads to arthritis but that has been shown to be untrue and nothing harmful will happen when you crack your knuckles.
The only benefit though you'll get from cracking your knuckles is to relieve tension and make your hands and fingers feel less stiff and painful.
But it's only a temporary fix.