Driving on a flat...al depends on the situation
If the tyres just de-flated or got a puncture, it should be ok for VERY short journeys, i.e. getting home or a garage.
If (like I did) you spin out and knock the tyres off the rims slightly, then decide to try and hobble home, it does damage them.
I didnt even get a hundred yards before the tyres had slipped virtually completely off the rims, was rollin metal on tarmac as I stopped at the side of the road
and now I'm paying the price as 2 wheels have small buckles in them and it knocks the tracking / allignment out
Need a new set of rims soonish