Liner socks offer minimal extra cushioning, but can make a great difference to comfort, particularly in very hot or cold temperatures.
Feet typically have 250000 sweat glands and can produce more than a pint of perspiration per day. Wicking liners with Coolmax fibres remove moisture from the skin on your foot, releasing it to the outer sock where it can evaporate. This reduces the softening of the skin and helps eliminate blisters.
In cold weather a Thermal liner traps a thin layer of dry air next to the skin, improving insulation.