For example, you want to use your MLB to cover the TE if he runs a route, but don't want your MLB to line up across from the TE in case it's a running play. You use this setting and the MLB will remain where ever you put him, but if the TE does run a route, then the MLB will cover from his current spot. Be careful with this as that TE will be uncovered for a sec or two until the MLB catches up with him.