That was true, many years ago. I cut it off when I lost what I had on top. I don't care for the Bald-With-A-Ponytail or Benjamin Franklin look. So I just keep it shiny all over. Easier to charge under a full moon.
Many cultures such as pre-Empire Rome, Japan, Native American, and others believed that hair was a source of either strength or magical abilities. I would add that keeping it healthy should also be part of this, trim your dead ends, eat healthier foods, since I healthy body overall produces better magical results. I think the length of hair is up to personal view. I've known people with short hair that can do some amazing things as well as people with long hair. If having long hair gives you that extra boost than keep it. If not then cut it. It's all about how you connect with nature and its endless possibilities. I hope this helps in some way.