No neighbor activate MP-BGP

[GabsC2]

Good day,

     I'm studying BGP and seeing the neighbor X activate and the no neighbor X activate. I'm reading about the reason for neighbor X activate but haven't seen the reason for the no neighbor X activate. Why do we need to deactivate the IPv6 neighbor on the IPv4 address family if I'm using the no bgp default ipv4-unicast already?

[MHM Cisco World]

if I am correct 
the reason is to prevent multi session 
where you can use ipv4 IP to establish multi session include ipv4 and ipv6 

MHM

[GabsC2]

Is that not the reason why the command no bgp default ipv4-unicast is used? To not establish the BGP neighborship using IPv4 unicast as default?