Note that was in 2009, as well. We've got a LOT more skins now than we did back then!
However, note he says you can't preload them all (which I don't enable) and they take over 3 GB... But that's a rare case where it's all skins in the game showing at once.
If you don't pre-load then yes you will get loading issues if a lot of colorful planes are flying around in visual display range. But if 90% of them use the same skins, theoretically speaking, the impact will be much less because it's using that same skin over and over, right?
Either way, practically speaking for me, skins don't kill my performance and I really enjoy winging with them or killing them. It really adds a lot to the enjoyability of the game. I think people that disable skins are missing out on more than half the fun.
How you use 'em is up to you, though.