I ran Z-Wave in a council building pilot, so here’s how I’d split it.
“Mandatory” is about certification: since April 2017 every new device that gets Z-Wave certified has to support S2, and controllers too. Your stick does. That doesn’t force you to include every node with S2.
The classes are S2 Access Control (locks, garage doors, anything that opens a door), S2 Authenticated (needs the PIN, which is the first 5 digits of the DSK on the device label or QR code) and S2 Unauthenticated (encrypted, but no proof it’s the device you think).
- Door locks: S2 Access Control, no discussion. Most locks won’t even accept lock/unlock commands without secure inclusion.
- Door sensors: if they only support S0 or nothing, that’s what they get. S0 is chatty (three frames per command), so I’d rather run old sensors non-secure than S0, unless they’re security-relevant.
- Plugs: S2 Authenticated. S2 adds a few bytes per frame, nothing like S0’s overhead. The traffic problem is the reporting interval, set the plugs to report on a 5 % change or every 60 s instead of every few seconds.
Keep the PIN sheet with the labels, you need it again if you ever re-include.