For many services, backup servers behave the same as the primary server when they are called upon to assume that role; however, in the case of the Edit Lockout Manager service, the designated primary server is required to perform online configuration actions. If only a backup ELM server is available, only operational changes may be performed on the application. If no server is available (neither the primary ELM server nor a backup ELM server), operational changes may still be performed on the local workstation, but they will not be propagated to the other workstations on the network until a connection with a server is established.
It should be noted that if one workstation has a tag locked, and another workstation does an operational change, the operational change will still be applied to the tag's properties, even if that particular property has already been edited by the lock-holder.
Information on operational changes can be found in Operational Changes vs. Configuration Changes.