I would like to be able to develop patches that create continuous, complex audio environments, where the output of sound does not require the initial triggering of an Envelope generator tied to a VCA. Very often I start with a single oscillator pure output, and then start applying successive levels of modullation and modification to it. In these cases, I do not want to have to keep hitting a keyboard to trigger an event, and using the other options of AM is always causing some sort of cycling of the sound's level. Then, I often take keyboard-triggered envelope generators, and apply them to parameters not associated with amplitude envelope.
I also think that this would make a good teaching aid for my music technology class: I think there is nothing better than straight modular synthesis to teach signal flow and interconnectivity of different module. However, by forcing the output VCA to be part of every patch, it is difficult for students to ingest the relationship between VCA and EG.