His alternative: Do what his job description says, surf the internet, watch the paint dry... sounds like a real recipe for motivation, excitement, and success.
2. You may open up more opportunities down the road. Going beyond what is required may get you noticed by coworkers that may prove to be in important positions to help you many years down the road.
3. You almost certainly will learn that way. By going outside what what is required you will put yourself in new positions and face challenges you wouldn't otherwise. This can be one of the best ways to learn.
If nothing else, it can help you be less bored then just doing the minimum required for a boring job.
2. It is a great way to establish good relationships that will help build your personal network for the future.
3. It may lead to unexpected good things happening with your current employer.
Why in the world would one want to do that? It's not like you are going to get paid more or get more free time for going the extra mile.