I would like to add a command by default , it is set protocols bgp parameters default no-ipv4-unicast when you want to configure bgp . I know the default behavior is enable the IPv4 unicast address family is announced to all neighbors , but it brings the following issues :
1-if you don't want to announce the ipv4 NLRI , you should apply it and reconfigure the neighbors .
2 -if the rules/route-map is not setting correctly , you can redistribute ipv4 prefix inside other NLRI(CPU-LOAD)
3- there many type the BGP NLRI (VPNv4 routes, VPNv6 routes signalling for multicast VPNs, FlowSpec information, ...),it would be a premature conclusion to assume that they using its BGP IPv4 session.
4- many vendors don't enable it by default (ipv4 announce)
example in FRR :
vyos# show running-config bgpd no-header frr version 7.5.1-20201222-185-gb3f4ff1d9 frr defaults traditional hostname vyos service integrated-vtysh-config ! router bgp 65001 no bgp ebgp-requires-policy no bgp default ipv4-unicast no bgp network import-check