If you are cleared for an instrument approach, you have to fly it, as depicted. Remember the IAP has the force of the FARs, as it is a FAR 97 procedure. If visual and cleared for contact or visual approach, you are OK to maneuver as needed, I see what you mean at KSMX, very steep final due to the antenna. It's similar to the controller, when spacing is getting too close, asking if the have the traffic or the field in sight, you do and he clears you for the visual. The visual eliminates his IFR spacing problem

GF