Client to Client vs Site to Site

Hi everyone,
regarding the wiregard server settings, what is the difference between the client to client and site to site option?
Thanks!

Allow the clients joined in this VPN can access each other.

About the Site 2 Site, it depends on the network applications, like if the GL GoodCloud S2S, it means allow the GL routers in multiple locations to establish secure connections with each other over Internet, including their subnet, auto advertise. Client 2 Client need to configure the route rule for each subnet.