What Happens If Laser Printer Paper is Used in Inkjet Printer and Vice-Versa?

Here are what will happen if you don't use the assigned printing paper to a printer:

There would only be less than good print quality because the coating on the laser printer paper isn't designed to absorb ink. It's designed to have toner melted on it.
If an inkjet printer prints on laser printer paper, it would result to a print that would easily smear or blot for the coating on the laser printer paper is not designed for ink.

Inkjet printer paper can burn in the laser printer because it's not designed to withstand the heat of the laser printer when it would melt plastic powder toner into text.
This burning can damage the inside of a laser printer.