To me it really depends on your project, how thick it is and what kind of fabric you use on the back. You absolutley need to lower them if you're quilting slippery or snag prone fabrics, otherwise they tend to get caught up on the feet dogs. If I have a really thin piece I'm doing I'll leave it up so it doesn't move around all crazy. If its thicker, I lower them as to not get any drag. As you progress you'll find what works best for you and your machine.