When you have your own IPv4/IPv6 address space, it's advantageous to announce it via your router to your ISP - especially if you have multiple providers (multi-homing). Even the lowest end EdgeRouters such as the ER-X and ERL can do a full BGP table.

The prefix lists are used to control what routes you get from your ISP, as well as the ones you send (announce).

policy {
    prefix-list BGP-ISP-From {
        rule 10 {
            action permit
            le 24
            prefix 0.0.0.0/0
        }
    }
    prefix-list BGP-ISP-To {
        rule 10 {
            action permit
            prefix 192.0.2.0/24
        }
    }
    prefix-list6 BGP-ISPv6-From {
        rule 10 {
            action permit
            le 64
            prefix 0::/0
        }
    }
    prefix-list6 BGP-ISPv6-To {
        rule 10 {
            action permit
            le 64
            prefix 2001:DB8::/32
        }
    }
}