The low speed network in a 2006 Cobalt* goes to:
Data Link Connector (DLC)
Body Control Module (BCM)
Radio
Vehicle Communications Interface Module (VICM)
Theft Deterrent Control Module (TDCM)
Instrument Panel Cluster (IPC)
Inflatable Restraint Sensing and Diagnostic Module (SDM)
Most of it is gone in the typical Goblin. Big thing it does/can do is supply data to the cluster that it receives from the BCM. Most of the data that the BCM relays on to the IPC is gathered on the high speed network. (RPM is a good example. ECM broadcasts RPM on to the high speed network. The BCM reads that and sends it to the cluster on the low speed network. And, voila, a working tachometer!)
It's worth noting that the low speed network is not a loop. Modules can simply be removed. Doesn't really matter how it's hooked up, unlike the high speed network.
*Others probably similar, I looked at a 2006 and 2008 Cobalt/G5 wiring diagrams.