I use mine all the time for paper piecing, wouldn't be without it. It has a ridge on the bottom that helps to align the ruler with the seam so you cut off exactly the right amount. But I don't know how you would use it for your courthouse steps. If the supply list simply says to bring it if you have it, then it sounds like it isn't entirely necessary. I would wait until class and see how the teacher uses it before deciding to purchase one. (Unless you also do paper piecing - then I would say to definitely buy that ruler!)