Gateway vs. Client Event Scripts
Your projects can execute scripts in response to a variety of events and actions that occur within the project's lifecycle. There are two major scopes for scripting: Gateway scripts and Client scripts.
Gateway Scripts
Gateway scripts execute on the Ignition Gateway, which means that they always execute in one place.
Client Scripts
Client scripts execute in the running Client, which means that they may never execute (if no clients are running), or they may execute many times. Client scripts will also execute in the Designer, but only in Preview Mode.
Because Clients are full-fledged applications, the scripts run on the computer running the Client, not on the Gateway's host server computer. This means that they don't have access to the Gateway's file system, and so on. It also means that if no clients are launched, the scripts will not be executing.
Note that these global project event scripts are not to be confused with the component event handler scripts.