Auto assigns that tech to any unit added to the lance, provided they have the time available.
So say you assign Jim Bob to your strike lance, all units in that lance are now assigned to that tech. Old techs should be removed. If you add Jim Bob to an empty lance then any unit added to that lance (or moved to that lance) will now have Jim Bob as the assigned tech.
I created this as a means to quickly develop large forces for those of us who use a single tech for multiple units. I like having a single tech take the maintenance role for a single force/lance rather than having one tech per unit. If you follow the reputation rules with say a company that is 12 techs, none of which has a full 480 minutes to do any given repair job. Using this, you have 3 assigned techs and 9 free techs that can do the hard work while still knowing the maintenance will get done by a qualified tech (I assign Vets for this role).
Hope that explains it for you, if not ask whatever is bugging you about it.
