APRS becomes a more useful expedition messaging service with the addition of SMS and email gateways.
These gateways bypass the traditional APRS messaging requirement that both parties be online at the same time. With the SMS Gateway and Email Gateway, I can send a message to someone back in the world, and the message will arrive on their computing device as normal SMS or email. Critically, both gateways store messages for 24 hours and allow receivers to request unacknowledged messages be resent. This means that someone can reply to my SMS or email at any time, even when my radio is off. I just have to turn on my radio at least once per day and instruct both gateways to send me any new messages.
I’m interacting with both gateways directly from my Yaesu VX-8DR but this thread on the Expedition Portal forums provides a good introduction of using them via APRSdroid.
APRS gateways also exist for weather reports, WhatsApp messaging, and requesting the nearest repeaters.