Some apps seem to reset their volume to 100% when started. It would be great that if the app was assigned to a current fader, it remembered the volume and set it immediately.
This would solve issues where a noisy game starts and you have to quickly jiggle the fader to get it to a reasonable volume.
There are also two levels on enforcement: one would be "initial" enforcement, ensuring that an app's volume is set to what MM remembered it as when it appears. The other is "consistent" enforcement, ensuring that all outside volume changes (i.e. non-MM) are resisted.
An interesting caveat here is that MM would have no way of knowing if the volume change was intentional (a user manually changing an app's volume in the Windows Mixer) or unintentional (an app resetting its volume), so MM would instead just have to blindly enforce the volume, essentially resisting all outside changes.
As such, enabling this on a group-by-group basis seems best with only initial enforcement. Consistent enforcement feels like it would just create more confusion.