Source-based routing is the complement to destination-based routing. The decision process for a routing rule is based on the source IP address. It is suggested to use this type of routing for all external traffic (Virtual Hosts or networks) and also for the management IP.
Using source-based routing, interface-stickiness of requests and responses can be achieved, which often helps simplifying complicated routing configurations. For example, source-based routing rules make it easy to define rules that send back responses to requests on the same interface (interface-stickiness). In absence of a source-based routing rule, the global (destination-based) default gateway may be used for routing responses, potentially sending responses over a different interface and thus breaking communication.