Central NAT vs Virtual IP

VIPs primarily used for Destination NAT translation, while Central NAT used for Source NAT translation. If for example you have a web or mail server that needs to be seen on the internet you use VIPs. Central NAT gives flexibility on how source address ( like internal addresses) will be translated going out the internet. You for example can define several internal addresses that would be translated to a single global address.

the central nat table is just another way where/how you can nat: You were used to do Source NAT with IP Pools and Destination NAT with VIP' s. the new central NAT table helps Checkpoint users to accommodate a bit faster on Fortigates :) ->I think its another part to help migrating Checkpoint configs to Fortigate. For example, the reason why Fortinet built the " any" Interface is the same.