Security Fabric Best Practice w/ Multiple Sites

In a scenario where you have multiple sites, separated by a WAN, is it recommended to create two separate Security Fabrics or can they be consolidated into a single Security Fabric group? Each site will have multiple FortiGates and there will be multiple FortiAnalyzers as well. I'm wondering if the latency/bandwidth between sites could become an issue with Security Fabric. Ideally, I would like to be able to group them all together. Thanks in advance!