Usually the main usage of multiSIM is that you can designate a phone as the phone with the primary profile (which receives incoming calls and SMS) and a 2nd phone with a secondary profile (for sharing data, it doesn't ring).

For MultiSIM you can change/swap the profiles of the phones (from primary to secondary OR secondary to primary etc) by entering some USD codes (via *100#) instead of physically swapping the SIM cards in each device. By swapping the profile you can make your previous secondary phone change to the primary phone without the need to physically swapping the SIM cards, you just enter some key pressed via USSD and voila it gets swapped.

But indeed this feature is not really used widely as primary devices remain primary, and secondary devices remains as such (for data sharing/leeching mostly). Having said that I've not tried before if my secondary phone will ring if my primary phone is turned off 

In any case, I'm using my primary phone with the primary e-SIM MultiSIM and my secondary device is using a physical MultiSIM card, so the MultiSIM works as an e-SIM as well.