I love to design things but I am a beginner. An app that has rulers and guides is easier for me to line everything up and ultimately it is one of the factors on which subscription I will subscribe to. If I am able to line everything up the overall creation will be better and helpful in the process.
Not only for aligning elements in a design are rulers and guides helpful but rulers are needed simply to see how large of a document you are working on. Being able to switch units of measurement is also so helpful with rulers: millimeters to inches, even picas and back again.