Phil:
The below information is on the Garmin website.
From these statements my understanding is that the tracking feature is something that you can turn on or off as you wish. If you choose to use it there is a $0.10 charge every time that it sends your track and location information to whomever you have chosen to share this information with, or every time that they request a location check on your device. If these are not features that you want to use, it can be be left turned off and there is no charge as that particular service is not being used.
I don't find their explanations of the inReach features to be very clear however.
Tracking
Share your adventures by sending track points at preselected time intervals. Using the MapShare™ trip-sharing webpage, followers can see your progress, ping your device to see your GPS location and exchange messages during your trip.1
inReach Tracking
You can use the tracking feature on your inReach® Mini 2 device to record track points and transmit them over the Iridium® satellite network at the specified send interval. Track points appear on the Garmin Explore™ website and the MapShare™ tracking page.