Explanation of CartDeliveryGroup in function input

[castles77]

Up until yesterday I had only ever seen one delivery group in the function input, but today I had a one time product and a subscription product in the cart and I see two delivery groups (not saying the functionality changed, just saying I saw it for the first time).

The content of the first group was both products in the cart. The content of the second group was just the subscription product. I would assume the type of the first group would be ONE_TIME_PURCHASE if that was available in the function input (like it is in the storefront api now). I would then assume the second group type is SUBSCRIPTION.

My guess is the discounts applied to the ONE_TIME_PURCHASE group affect the shipping on the current order and discounts applied to the SUBSCRIPTION group affect the price of shipping in recurrence orders. Can anyone confirm that is correct or point me to some documentation?

Also, are there any other scenarios that result in multiple delivery groups?