You can of course have instances of these modules in the same diagram as MIDI or others. This demonstrates how Weaver modules pay attention only to data of relevance to them, ignoring the rest.
The Counter is actually a little more versatile than that, in that it will count any kind of Weaver packet that flows through it. See its description for details.
In addition to showing the actual integer values of such packets, the Counter will count packets of any type. Each time it sees a packet of any type but PacketSource, it adds one to the currently displayed value and shows it in blue. Note that this is not independent of data received from a packet source -- it simply counts from the last integer that arrived (initially zero).
Counting packets can be useful to ensure that data is flowing when and where you expect it to (when you split a MIDI path for example), but be warned that the Counter was not built for speed. It simply holds on to the packet while it updates the window (although it doesn't necessarily update on every packet if they are arriving too fast). This means that perhaps you shouldn't expect glitch-free audio if you include a Counter (with an open panel) in the path.