Spanning Tree Protocol (STP) is a loop avoidance protocol. If your network does not have loops, you do not need STP. However, you must always enable STP. If you do not enable STP, all traffic stops on the network with a loop or with the wrong cable plugged into wrong ports.
However, STP is slow to converge after a network failure and provide a new port into the network. By default, the speed is ~50 seconds.
A modified version of STP is the Rapid Spanning Tree protocol. Rapid Spanning Tree converges faster than STP and enables new ports faster than the older protocol. As the Rapid Spanning Tree protocol works with all Avaya equipment, use the Rapid Spanning Tree protocol.