We've taken several precautions to try to prevent excessive cellular usage. First, TerraGo Edge only syncs notes that have been updated, never old unchanged information. Photos, videos, and offline maps are only synced the first time. Photos taken in Edge are compressed to JPG from the raw PNG file, bringing a typical file size down from 12-13mb to 2mb or so.
For those using online maps (openstreet maps, mapquest, etc), we use Mapbox to cache the tiles for a short amount of time to help prevent re-downloading redundant tiles. The most recent 1000 tiles viewed will remain in your offline cache.
For those that want zero data usage, a notebook could be loaded up ahead of time with an offline map, and all data could be collected in the field in airplane mode. You would then sync the data back to the server later when you have wi-fi access at your office/hotel/etc.