Why do you need a secondary connection in routers?

Question

Computer networks

The provider advised for the stable operation of IPTV in the router settings to check the item "secondary connection" in TP-Link. Mikrotik has a similar setting - DHCP client.
Please tell me how this will affect the security (visibility) of my devices in the provider's local network?

Answer 1

It does not affect security in any way. Your ISP devices will remain behind NAT.

Answer 2

some providers give the client a gray address via dhcp to access internal resources and access the Internet via pppoe/pptp/l2tp