Because that's the reason why you are using bitcoins. I could tell you that bitcoins are great for international money transfers or that it is a technological/social project with many interesting cryptography concepts, but why would you or your parents care?
You do not need to make international transfers, you certainly are not studying any of the underlying technology and you should not be making high risk investments if you are young and you do not have your own money. That's why your parents cut your allowance and they did great.

You should only be spending money you don't need with bitcoins. Money you don't need is something that you don't have, because you do not work to earn it.