Answer's thigh-high socks provide a complete knee brace sub-layer offering maximum shock absorption, warmth and comfort plus three ribbed stretch panels at the instep, ankle and cuff to hold socks in place.
Thinner sections on top of foot provide more sensitivity through the boot for better feel of control levers.
The "thinner sections on top" wore through quickly by my shifting toe. Keep your toenails filed and your boots tight... or just buy the MSR Moto Soxx instead. I bought those too and they perform much better.