Can someone please tell me how to use and the purpose of the group filtering on the APRS group filter menu.
Normally, your TM-D710GA will only display APRS messages sent to the call sign programmed on the radio. The group filter option (menu 623) will allow messages sent to other destinations to be received and displayed by your radio. A few are included by default, and you can edit the list to add others - or remove what's there already.
Some stations may want to send out news to anyone within the range of a digipeater, or group of digipeaters. This is where a message sent to ALL might be useful. If you're working as part of some event that is using APRS messaging, there may be other group identifiers used for those messages.
73!