Last time we checked this (which was maybe 8 months ago) these were the findings:
A track point feature is approximately 930 bytes when uploaded via applyEdits. There is around an additional 1kb overhead for the request and a minimum of 150 bytes for the response.
The number of points recorded varies based on the movement of the device. 2000 points per hour would be a reasonable average estimate. If we assume 350 points uploaded every 10 minutes (default behavior) that would be around 325 kilobytes per upload which would be around 2 megabytes per hour.
If the default LKL update frequency of 60 seconds is used that would be 60 * (930 +150) = ~65 kilobytes.
There are also other requests made which are generally small and negligible when compared to the track upload.
So I would say to expect around 2 megabytes per device per hour. Anecdotally, this seems to match what I see on my phone from tracking a few hours yesterday (5.7 MB).
I'm curious if other people have data usage metrics.
