So I got into a discussion today in the Barrens because I said that I don't use an ammo bag because I'd rather have more bag space and the 10% buff wasn't good enough to give up the bag space. Everyone acted like I was crazy.
Edit - I am only talking about leveling - not end game. For clarity - having more bag space means more gold which means a mount at 40 which means faster leveling. I don't think a 10% buff makes up for the gold I gain by being able to sell more things.