Licensing in is based on the number of nodes and the number of technician logins.
Active IT assets such as workstations, printers, and servers are considered nodes and take up a license.
You can add any number of ServiceDesk Plus but the login permissions are based on the licenses purchased. 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.