Wide handlebars are useful because it gives your arms extra leverage. When moving on rough terrain, it makes it easier to keep direction.

How about I make my current one shorter and buy a new one if I ever decide that I need a longer one against.

 

So the stronger the rider is the more narrow the handlebar can be?

I guess? But, handlebar also needs to be wide enough for your shoulders. Idk about the required angles but consider, that stronger riders will probably also have to hold their arms wider...