Appliance notifies Orchestrator when a configuration change is made. If for some reason the change events didn't reach Orchestrator, Orchestrator can call this api to get any configuration events that it missed

Think of appliances changes as subversion changesets. Appliance is at a certain changeset and Orchestrator servers have to make sure they do updates to get the latest changeset. Orchestrator can query appliance to check if there are any missed event by providing a start and an end change set number