Apart from sports grounds, when performing labouring duties and on the beach, socks are meant to be of knee length.   A man of style does not expose his legs to others. 

This is the length of dress socks to wear when wearing a suit; it is the length to appear properly and professionally dressed, as we do not want to show our legs.

Discreet ornamental designs at the side or at the ankles of socks are called 'clocks.'

Sock with clocks are a bit less elegant or formal than plain socks, are are inappropriate for White Tie or Black Tie, but go well for plain dark business suits or similar professional suits slightly less elegant, e.g. discreetly patterned suits with pinstripes or windowpanes.