there are several.
1. automatic actions from another system. for example sccm finds a machine not running the latest version of a mfe product, it applies a tag to the system called "install X" via the api. that tag has a deployment task associated with it
2. farming out repetitive tasks to another group. for example help desk is assigned with remediating callers that think they are infected, using a web interface they can assign the "infected" tag to the machine
3. running simple reports thru a web interface. you dont want to give access to epo for your mssp so you give them a front end via a web server to run reports