http://www.macrollc.com/FAQs/FAQ-sonicwall_user_licensing.htm
Many partners have asked how SonicWall deals with the number of users in appliances like the Tele3 and Soho3. When the SonicWall is turned on, it “listens’ for broadcasted IP addresses on the LAN port. As the firewall hears new IP addresses, it puts them in its licensing table on a first come basis. These addresses do NOT necessarily come from hosts that have accessed the WAN or Internet through the firewall. Any addresses that are discovered after the license table limit is reached are blocked. The SonicWALL will block these addresses from communicating on the LAN by responding to ARP requests for that address with its own MAC address.
So this means that network hosts such as printers and files servers will use up node licenses on the SonicWall, even if they do not go through the firewall. It is possible, however, to create an Access Rule(s) that prevent IP addresses from counting toward user licenses. If you want to exempt a printer from the license count, create an Access Rule that DENIES the DEFAULT protocol from a source IP of the printer to a destination of the WAN. From that point on, the SonicWall will not count that IP address in its licensing table.