Being someone who loves to learn about anything she can, I can personally tell you that there is NO such thing as useless knowledge. Every piece of knowledge you know can help you, whether it helps you strike up conversation with that hottie across the room, or saves your life. Everything matters. Everything is important. Learn everything you can about everything you can, because it can and will help you somewhere along the way, maybe it will do you a small favor, or maybe iit will be the difference between life and death. You never know, so prepare yourself with as much knowledge as possible. You might not agree with me that everything is important, but if that's your opinion, what have you lost by learning it? Nothing. What could you lose if you thought you didn't need to learn it, but you actually did? Your very life may be at stake at that point.