Superchargers are for free long distance travel. So, if you drive over 200 miles in a day and Supercharge, they are free.
But if you drive under 200 miles in a given day and Supercharge, Tesla can bill you.
Since Tesla can't legally bill for electricity, DON'T.
BUT Tesla can bill for changing your display from a low battery status indicator to a full (or whatever percentage) battery status indicator.
(Re: the lingering question of Model 3 Supercharging)