Does Limiting Magazine Capacity Matter?

On a handgun, a magazine change takes less than a second.  Ditto for an AR-15.

I am hard pressed to see how adding a second every 5 or 10 rounds matters.  Even careless unaimed fire is about 2 shots a second.  Adding a second every five rounds reduces effective rate of fire by about 20%.  Every 10 rounds, about 10%.  

This is not a solution.  Banning detachable magazine weapons might reduce mass murder death counts, but I do not think 100 million Americans are going to be alright with that.

Furthermore, there are defensive uses where having 15 rounds without having to reload makes great sense.  Three home invaders, for example.   Not every shot you fire will hit your target or necessarily be sufficiently incapacitating.