I have read on multiple sources that the Sandy Hook shooter, while he had a large number of 30-round magazines, did not shoot any of them to empty. Reportedly, he shot about 15 rounds from each magazine.
Speculation (which I believe was attributed to the CT State Police) was that he was so accustomed to playing video games in which it's good strategy to do "hot" reloads when transitioning from one room or space to another that he more or less defaulted to doing the same thing in real life.
Okay, so 15 is more than 10 ... but it's half of 30, and it makes the fact that he was carrying 30-round magazines IRRELEVANT. If he could kill 26 people with mag swaps every fifteen rounds, how many lives could realistically have been saved if he had to swap every ten rounds? Probably ... none.