Heavens sakes - we don't need rulers at all! Quilters used to just cut out pieces of fabric and make them fit. Or use templates made from used cereal boxes. I'm sure there was once a discussion of "why do we need this pizza cutter thing when we have scissors!"
Haha! But don't ask me - I'm a sucker for a new ruler or template! I love to have a variety of tools and if one of them helps inspire me to make something new, then I'm in!