I think I need a ruler like that just because it's a lovely thing... all wavy...
This was actually on the second ever ruler I had bought, and its done me fine. I tend to use the "bigger/longer" wave side. I tend to find the smaller ones are a bit tight for the walking foot to negotiate. I find these are a simple way to quilt a log cabin or 9 patch ..... just enough to hold down all the seams. I don't even measure, I just eyeball it, and then draw the lines in with chalk (dark fabrics) or water erasable pen (light fabrics).
It creates a nice effect .... this is just strips of xmas fabric, with some wool batting and insulbrite batting, made into a trivet/bread basket.
Trivet/Bread Basket by
Dani, on Flickr