A "Digital RX Group List" allows you to create a digital scan list that will listen to and receive any digital contact in the list without having your radio set to that specific contact. For talkgroups this is very handy in the case where someone may be on a different TG then you are using. In this case if you have a group list set in the channel configuration for the channel that you are using and someone is on a different TG on the same time slot (TS) and their TG is in the group list set in your channel configuration then you will hear the traffic on that TG.
On an MD-380 the "Digital RX Group List" will hold up to 32 contacts, but since a ZONE will only hold up to 16 channels I suggest creating a group list that matches the 16 channels in a ZONE and add that group list to each channel in that ZONE. That way when you are in a specific ZONE you will always hear any traffic on the 16 channels in that ZONE, assuming all the channels are on the same timeslot.
73,
Ken - KA8OAD