Rob Pincus explains the advantages of a muzzle low ready position, especially in an extreme close quarters situation. The low ready position allows for more efficiency and consistency when moving into a shooting position and for dramatically more control if your rifle is ever grabbed by an attacker.
Student alert! If your defensive firearms instructor is not giving you an integrated system of firearm manipulation techniques but rather a set of unconnected techniques that don't integrate well together, don't reinforce each other, and don't contribute to your efficiency by being consistent with one another, you need to challenge those techniques.
Old-school thinking held that if a tourniquet were used on an extremity wound, the injured person would lose that limb. That has been shown to be incorrect, and tourniquets are now in the first-aid kits of medics on battlefields and streets worldwide.