We are not very sure that it would still work if there's no app id specified. Please let us know if we are not getting this correct.
We feel the app id is required for following reasons:
**Builder Mode**
1. To get information about the webmap and variable(s) configuration settings
2. To check if current user is owner of the app
3. To save changes back to the app
**Public Mode:**
For public mode, the app id is required to get information about the webmap and variable(s) and other  configuration settings.