Any asset with the product type as IT asset is considered as a node. The nodes are automatically discovered during the scanning process, and takes up a license in ServiceDesk Plus. Some of the examples of nodes are workstations, servers, printers, routers, switches and access points. If an IT asset is moved to "Expired" or "Disposed" state, then the asset will not be considered as a node and hence will not take up a license. But the assets will be maintained in the system for historic data purpose.
You can add unlimited number of technicians in ServiceDesk Plus but the login permissions provided to these technicians is based on the license purchased. Say, you have purchased license for 10 technicians, then only 10 technicians, including the default administrator login, will be able to login to ServiceDesk Plus and work with the application. The remaining technicians will be considered as Non-Login technicians. These Non-Login technicians will not be provided with login permissions but you can configure to send SLA violation emails, group notifications and scheduled reports to these technicians.
A typical case where Non-Login technicians can be used is for your Field Technicians, who need not log into the application but be notified about the issues assigned to them. When a request is assigned to these technicians, a notification is sent via email from ServiceDesk Plus. On completion of their job and replying to the notification email, ServiceDesk Plus will append the reply as a conversation in the original request automatically.