Are Sessions needed for networking?

Hello,

I have a question regarding Sessions and Networking. If I dont use an OnlineSubSystem but have my own Master Server do I need to create Sessions?

I start a dedicated server and send the IP to my Master Server the Master Server send a list of running servers to all clients. Then I join with ServerTravel.

As I see it Sessions are just used by the OnlineSubSystem but have no impact in actually hosting/joining a server am I right? Or should I use OnlineSubSystemNULL
and start sessions.