What would be the thinking or to help my understanding, behind
choosing to set <all interfaces> instead of using specific interfaces
(Private or Public) when creating an exception.

Example:

<all interfaces> as the source interface
<Public> as the destination interface

vs.

<Private> as the source interface
<Public> as the destination interface

Note: This is assuming you have a 3rd interface being the VPN Tunnel
Binding

Thanks