Overly aggressive calling has saved more bucks lives than just about anything else. Aggressive calling is only used when bucks are a long ways off. The buck has to hear your call in order to respond.
If a good buck is responding to your call, shut-up. If he stops or hesitates, try a few subtle calls. A few doe bleats will often get a buck that is hung-up to begin to move in your direction again. Don’t get forceful with your calling until all else has failed.