The controller structures (all of them) output the contents of the logistics network from the wire connection. Since this is the same connection as the controller's input, the entire content of your logistics network gets fed back into the controller every update. This does two things:
1) It creates a lot of lag since each controller needs to iterate through the entire content of the network each update. As an example, 5 controllers of any type takes me from 60 ups to 30, if they're in my network area.
2) It renders unit data controllers useless as all of the item signals get passed from the controller back to itself.
