You need to sand them to smoothen them out and the wax acts as a lubricant so the gears can slide and move freely against each other. If you don't do these steps, the gears may have a tendency to get stuck.
@slayerxsosa From my experience, usually if the kit is imported from China, there isn't any wax included unless the store is based locally. But you can also use candle wax if it's not included.
I agree. You just have to do a little fiddling to get the pegs in but otherwise it's smooth sailing all the way. It might have looked simple in the video because it was edited to look seamless. 😊