What is the function of relay in node features BLE Mesh

Good day,

Recently we've rolled out a mesh network with about 400 nodes. As we are quite new to this, and the firmware was quite rapidly developed by an outsourced developer, I was wondering: During provisioning using the nordic app, we get to see the node features: Relay, proxy, friend, low power. The first two, relay and proxy, were not enabled, and the last two were not supported. At first I was worrying that since relay is turned off, the nodes would not relay the network layer messages, but after extensive testing, we came to the conclusion that they must be relaying because the furthest away lights only respond to commands if lights in the path between the client and server are powered on. If not it would not respond.

Can someone explain why there is a specific node feature called Relay, which without it messages seem to be passed on between nodes anyways. Is this maybe a relay on the application layer? Or does it influence the TTL of a message?

our network consists of NRF52840 nodes.

Kind Regards,

tmennink