Without saying I disagree with someone specifically, there is no reason to ever call to a bull until you have to. Meaning if you can kill a bull without him ever knowing you're there that is ALWAYS the best bet, and will most often give you a better shot. You can always start calling if you have no other options, but once you start calling he knows "something" is where you are at. Once you've done that you have now limited your options. If he has no idea you are there you have every option in the book still available to you. If you are just looking to kill any bull, then sure you can call bulls in all day. I'm personally only ever hunting herd bulls. I don't want to call in any other bulls that may be in the area. What you described is my dream scenario. Stationary bull that is being vocal. He is asking to be stalked in on and killed or set up on and waited out until he makes a mistake. You start calling and you just put a lot of your success to chance and or his behavior to the calls. I like to be in total control 
