A question from my text is:

The simultaneous equations $\displaystyle x+2y+3z=13,\;-x-3y+2z=2$ and $\displaystyle -x-4y+7z=17$ have infinitely many solutions. Describe these solutions through the use of a parameter.

I understand how to do this. I just don't understand the purpose of using a parameter?

Thanks for your help :)