SEP will use 1 license per machine. Unless it's a virtual platform then it will consume multiple licenses so for eample if you have 10 people that log onto a virtual machine SEP will allocate 11 licenses (1 for the physical machine and 1 for each of the virtual environments that have been logged onto).
If you have your SEPM to delete offline machines after 30 days if nobody has logged on that machine or virtual environment for 30 days then the SEPM will release that license back to your pool of licenses.