Actually loco links are formed and those are usually not disturbed because pairing and unpairing of locos is done only in the shed and hence the arrangement is not disturbed. Wdm3A couple locos can be used to haul freight loads over flat gradient as well and come in handy for that purpose and hence almost all Wdm3A are coupled unless their link is connected to a passenger train and layover period is so less that it can't be used for anything else other than shunting.