Danger is that you put all the weight back in again with the cage!
I think SteveL's race car was about 1300Kg, so a saving of 250KG.
He had a full cage but the car was absolutely stripped.
Lightweight bonnet, carbon hatch, plastic windows in fixed position so no electric motors in the doors, the dash was just the shell with everything removed internally with carbon panels and light digi dash. Door bars were cut out and all the sprayed on noise insulation stuff was chipped off too. All the heater stuff was removed and he fitted a heated windscreen to keep it road legal!!!