I have an Astaro ASG V7 firewall. When we use the Masquerading NAT only, we can not access our own web servers, which sit behind the ASG. When I setup a SNAT rule and map it to Network>Interfaces>Additional Addresses, I can access our web servers. Of course we can access our web servers from inside using the private IP's, but not by DNS name which is public IP.
This description is our inside network only, it does not affect external traffic from the internet.