security fabric connection in fortigate

The Fortinet Security Fabric spans across an entire network linking different security sensors and tools together to collect, coordinate, and respond to malicious behavior in real time. Security Fabric can be used to coordinate the behavior of different Fortinet products in your network, including FortiGate, FortiAnalyzer, FortiClient, FortiSandbox, FortiAP, FortiSwitch, and FortiClient Enterprise Management Server (EMS). Security Fabric supports FortiOS 5.4.1+, FortiSwitchOS 3.3+, and FortiClient 5.4.1+.

Ref: https://docs.fortinet.com/document/fortigate/6.4.0/ports-and-protocols/339062/fortinet-security-fabric

Security fabric connection service is enabled to have downstream devices (devices connected to this port) to join security Fabric.

ref: https://community.fortinet.com/t5/FortiGate/Technical-Tip-Configuring-the-root-FortiGate-and-downstream/ta-p/192156

if you don't have security Fabric setup on your network, you don't need to enable this service.