How would you explain the benefits of saving money to a teenager?

Give them pocket money, and if they want to buy things of their own (such as phones, gaming consoles, etc), they gotta save up.

Also try to explain the concept of compound interest. Not sure how receptive they'd be though.

I started saving prior to University as I needed to pay for my university studies and refused to take on any debt. Thus, saving money as early as possible is something that I am a strong advocate of, and also passionate about.

I always reference Burton Malkiel, the author of A Random Walk Down Wall Street. He describes the power of compound interest here:

William, starts saving $4,000 a year when he is 20 and stops after 20 years, after having saved $80,000. His brother, James, starts saving $4,000 at 40, and does so for 25 years, for a total of $100,000 saved.

They each earn 6% on their savings.

At age 65, William will have $850,136 in his account, while James will have only $219,242. Despite having saved less, William's nest egg will be almost four times greater because of compounding.

TL;DR: Start Early.