Why do people study Latin if it is a dead language?

Wouldn't it be more useful to study a language that is widely used today?If you have studied Latin let me know how it benefited you or if you felt it was a waste of time.

My dad doesn't like for me to be purchasing products--even books! He thinks they're a waste of time...so is it possible for me to learn Latin efficiently without purchasing anything? If so, how? What links do you recommend?