Hello,

Checking this box means that you can call the server action externally using a public URL. Obviously security considerations apply (e.g. if your server action's code contain a sudo(), this might make some sensitive information accessible externally, etc.) but otherwise can allow external hooks to trigger code internally (the way you would do it with a route controller if you were writing code).

You can get some information about that in the tooltip of the "Available in website" field.

Hope this helps :)