The use of SLA targets is specific to certain SD-WAN strategies. The "Lowest Cost (SLA)" and
"Maximize Bandwidth (SLA)" strategies are explicitly designed to use the configured SLA targets to make routing decisions. The "Best Quality" strategy uses performance metrics but does not necessarily require or reference SLA targets in the same way, while "Manual" does not use metrics at all for path selection.
This is a core function of SD-WAN rules with SLA targets. The purpose of configuring an SLA target with specific thresholds for latency, jitter, and packet loss is to define what is considered
"acceptable" performance for an application. SD-WAN rules then use these targets to check if the members (interfaces) meet these requirements before a flow is steered over them, ensuring that a preferred path still offers a good user experience.
FortiGate allows for a single SD-WAN rule to reference multiple, different performance SLAs. This is crucial for complex deployments where a single SD-WAN rule needs to handle traffic for multiple applications that have distinct performance requirements. For example, a single rule might direct VoIP traffic based on one performance SLA with strict latency/jitter targets, while simultaneously handling general web traffic using another performance SLA with more lenient requirements.

The destination IP 10.2.5.254 falls within 10.2.0.0/16, which is covered by SD-WAN service rule
4. The output of service rule 4 shows port2 as the selected interface, which FortiGate uses to steer the traffic.