The title not make much sense but what I am thinking is to allow you to tie units together (more than just boats and trailers) so that they always run together if you send one.
I am thinking something similar to how FDNY Squads and HM1 work. For those that don't know, Squads run as 2 units to some calls, the engine and the squad. Hazmat 1 always runs as two units, the walk in hazmat unit and the other unit (cant remember what it's for but most likely extra hands and equipment).
I think it might be a cool addition to allow you to tie a maximum of two units together so that they always run, this is not an alarm response regulation, this would be similar to tying boats to trailers and stuff like that.