SNAT and NAT are similar, except SNAT does not accept devices that initiate inbound connections. SNATs are used to change the source IP address, specifically to force the L3 return path for response traffic through the load balancer when routing from the real server back to the client's real address would bypass the load balancer. An example would be that you want to load balance a server where the server's gateway is not the load balancer.
NAT also IP address translation, in the case of F5 they are mainly used to provide administrative access to backend servers via the load balancer. For example you may have a private non-routable network on the load balancer but you need your administrators to RDP or SSH directly. So you would use a NAT where from the routable address it can be reached.
I am sure there are examples but this is what is typically used for.
Hope this helps,
CB