[Samba] Samba4 security issues

[me at electronico.nc]

Hi all,
Could someone explain this sentence on the Samba Wiki ( 
https://wiki.samba.org/index.php/Samba4/HOWTO/Virtual_Private_Network ) :
"Plese note that the Domain Controller (Samba4) can also be configure on 
the Firewall itself, but this is strongly not recommended due to a 
security issues."
Are these security issues still there when Samba is listening only on 
LAN port ( https://wiki.samba.org/index.php/Samba_port_usage ) like :
bind interfaces only = yes
interfaces = lo eth0
Of course server is well firewalled and remote users are connecting 
through VPN.
Thanks in advance for your time.
Nicolas