If you are wearing boots rather than trail runners, I would recommend a double sock even in the summer. There are two reasons for the classic wool outer sock, poly liner sock. One is moisture management. Poly wicks away from feet, wools provides insulation and buffering.

The second reason is that the typical boot doesn't give or conform to your foot, so when you are walking there is a bit of friction. The double sock typically puts the friction between the socks, rather than between your foot and the sock. [BTW: best to have the more textured part of the wool sock toward the outside of the boot, smooth facing inward which often means using wool socks turned inside out.]

--Mark