Also, bandwidth can still be pretty expensive. Mirrors mean they can have you use bandwidth from those folks who provide it for free for projects or from project sponsors.
Those who aren't seeing the behind-the-scene views don't realize how much bandwidth can cost - especially if your download is popular. Also, not all bandwidth is equal. Some hosts are more reliable and faster than others. Then, there's locations issues. Countries l like AUS or NZ have high bandwidth costs when compared to the US, because they're island nations and there's a finite number of bits they can fit in the lines.
I pay for bandwidth for a number of sites. If it's busy, it can total a pretty impressive bill.