Would there be any reason to have more than 1 IP address allocated to a Server? Would there be any reason to allocate an IP per Role for example? From what I am understanding of the architecture, there doesn't appear to be any reason to allocate any more than a single IP address to a Server but if I am missing something, would appreciate some insight.
IP addresses per server
From experience with other control panels the primary reasons would today be 1) offering multiple outbound IP address for mail services / mail service IP clustering, so you can remove and manage their reputation better (personally we'd move this out to its own postfix cluster and smart host everything via that) or 2) spreading some DDoS risk by having some customers using different IP to others meaning when your upstream blackhole that IP due to volume the others continue working or 3) in niche scenarios where the services connecting do not support SNI or 4) when moving customers or combining servers you might not be able to re-ip the customers custom dns so consolidating multiple servers could be useful or 5) if you want to do some things internally like backup to SAN over LAN, probably some others I forget. Not sure the specific use case intended though.