What if you draw one and your audience, customers or the people you care about are on the other side of it? What if you offend or turn off the people you're trying to serve? What if people see the real you and your true expression, and simply aren't interested?
Most lines in the sand come from opinions on self-expression -- which isn't a necessity. I don't have to swear in books. I don't have to talk about feminism if it's not my job. I don't have to be public about my passions, pet rats, or vegan ramblings.