A Sniffer details packet transfer, and thus, a Sniffer trace analysis can help pinpoint switch and Trellix IPS performance or connectivity issues when those persist after you have exhausted the other suggestions in this document. Sniffer trace analysis reveals every packet on the wire and pinpoints the exact problem.
Note that it may be important to obtain several Sniffer traces from different ports on different switches, and that it is useful to monitor ("span") ports rather than spanning VLANs when troubleshooting switch connectivity issues.