Short and simple. What would happen if you accidentally switched the live and neutral wires when wiring your home electricity into the distribution board?
There would be a shock hazard, and some devices might not work correctly. Depending on where exactly the wires are flipped, ground fault detecting circuit breakers may become ineffective. All around, this is a bad idea.
not a good idea. A short circuit with a poor contact becomes a fire hazard.
But if just connecting an appliance temporarily with a 2 pin plug , possibly nothing.
In my previous home I found installers had used Neutral to box ground for a stairway switch, when I converted it to a 2way switch. Neutral is grounded in or outside the home at the distribution transformer and ground is a safety wire that also carries Line filter cap currents up to 0.5 mA each.
Old TV sets once used 2 prong plugs polarized and a neutral grounded chassis.
The potential (no pun) for hazards is great but in theory it might not matter under very limited circumstances.
2 prong plug for outlets are polarized in America for a reason for some products which rely on neutral being near 0V for winding insulation proximity to metal case.
Such as; the metallic Edison socket being neutral with the centre contact being switched line. If your reversed L-N and switched off the lamp, the metal collar would become unswitched Line.