A great trick to prevent paint getting on things you would rather not get them on. Sometimes painters tape isn’t the easiest to cover some items and foil seems to mold to whatever it is placed against. Even better, use the dollar store cheap thin stuff to mold even better. For door knobs, loosen the screws and tuck in foil and squeeze to mold to door knob shape. Can you think of any other ways foil could be used when painting to help not make a big clean up?