I was certified in FortiNAC (Part of Fortinet-NSE6) last year and I've personally implemented FortiNAC in three organizations. We work as a team with people who have expertise in different areas and Vendors and have exposure to different infrastructures.
FortiNAC scans your network to discover every user, application, and device (IOT), With up to 18 different techniques, it can then profile each element based on observed characteristics and responses for granular visibility - We then apply state-based control(eth0 VLAN switching) and Policy based control rules for access control and response.
Anyone (Domain users, Contractors, guests, etc) wanting to connect to the network has to be accessed by the NAC. Users come in at different times and some may be working from branches or home through a VPN and they will be authenticated in the same way with different privileges on the Network.
So it has to run 24/7. It's authenticating users all the time. We are gold partners with FortiNac.