Some may not be able to read a scale…
I know someone that received an overfilled tank, it blew off in the back of his van, scared the heck out of him!
Pretty much impossible now with the OPD installed on all DOT approved tanks.
Some operators may not look at the tare weight stamped on the tank, causing inaccurate filling when using a scale.
In a perfect world, every propane supplier would charge by the gallon instead of charging the same flat rate whether the tank is partially full or not. Apparently, there are a few that will do this for grill sized tanks. (but not around me!)