The use case for this would be to allow public users to access resources on an Enterprise in the same way as arcgis.com.
A specific use case is to provide public users with an offline map (through Explorer) and access to a form (through Survey123) from Enterprise. The only way to do this with Enterprise is, as far as I can figure, by side-loading both a .mmpk and a survey on a device which is not a very user-friendly method.
The limitation is in the Explorer app, which by default connects to AGOL and there is no way to connect to an Enterprise without signing in.
Survey123 has the ability to connect to an Enterprise portal without signing in, just add the portal URL and leave it as the active connection. Implementing the same function in Explorer as in Survey where you can add a portal would solve this.
Since both public surveys and public MMPK’s are possible to use it seems logical to allow this functionality through Enterprise as well as arcgis.com.