The Fog Bank in Stealing Creation is used to avoid enemies. It can be used simply clicking in it, making pickpocketing easier for either team as well as avoiding enemy attacks. This tactic is very common and should be used if the player: A) is gathering supplies and is nowhere near a barrier or home base. B)if under attack or being pickpocketed several times by the enemy. Or C) if the player is low-leveled and is doing either A or B.
This bank can be useful to one's team, and harmful to the others. Be cautious though, as you cannot attack, pickpocket, or follow others in the fog bank. On the mini-map, all characters, friendly or not, appear as regular people (White circle dot). Try to use this only when necessary.