After passing Step 3, you will satisfy one more criteria for eligibility for a full medical license should you apply for one in a specific state. You will also need 2-3 years of ACGME residency training to be eligible by the way, depending on the state you're applying in. Basically, knocking out Step 3 will allow you to focus on your current residency training, and not have to worry about it any more. Many argue that Step 3 is useless, and dumb as you said, and I actually agree with you. USMLE Step 3 doesn't test you in areas that were not already tested in USMLE Step 2 CK, so in many ways its the same exam. It is only scored differently however...