"1. Abrasion: because I don't get out enough to toughen up my feet so, I need that layer to avoid abrasion.
2. Warmth: Of course this doesn't apply to summer - but wait, my socks stay wet for a while after crossing a stream and that definitely cools my feet.
3. Cleanliness: Socks keep my feet a little cleaner than without.
4. Cushioning: Just because I like cushy stuff :)
I'm sticking with my socks!"
+1, but adding the stink reduction. I don't know why feet stink less in shoes with socks, even plain old cotton socks, than without. I've had to scold my kids after going out for a few hours geocaching or what-not because they'd go without socks, against my instructions to wear socks, and take their shoes off in the car on the way home. Omg, thier feet stink! Not only that, I don't know where you hike but where I live, you go out for a while, your shoes get fine grit in them through the mesh, which builds up and feels like sandpaper against your skin. Socks help protect against irritation.
I'll go sockless if I need to run out and take the trash out or get the mail. Anything longer, and I'm wearing socks.