Ones first reaction is to add this to the file marked Nude sleeping." As in, Youll be warmer in your sleeping bag if you go to bed naked." A notion that has absolutely no basis in fact.
Pearl Izumi Attack socks
But in this case, there may be some truth to this statement. Mainly, going sockless means your shoes have the task of absorbing perspiration. And sweat has salts and acids that can damage leather and fabric. So if you bike a lot and sweat a lot, then its possible that the shoes will not last as long as they otherwise would. Will there be a big difference? Very hard to say.
I also dont know if there would be any wear" difference, in terms of actual physical impact on the leather in the shoe. I should think your own skin would start to wear away before the shoe leather would. But I could be wrong about that. Certainly socks are softer than your skin, so protect both your feet and maybe the shoe as well.
You can go sockless and still protect your cycling shoes by taking the simple step of washing them out occasionally with a little warm water and maybe a squirt of Dawn detergent. That will get the acids from sweat out of the shoe.
And if you just dont like socks, maybe try some Pearl Izumi Attack socks ($7; pearlizumi.com). Theyre a really light, thin cotton sock that is almost like having nothing on your feet.