Why it is good to have a hobby?

Me and my colleague went to see my advisor's band performance just now. My advisor is darn talented in singing and playing musical instruments. Before I went to this bar to watch his band performing, I always think of him as a research scientist who only deals with academic stuff, intelligent, complicated stuff...After watching the performance, I can see that my advisor is not a nerd.

I guess it's important for every human being to have a hobby. Hobby in sports, or musics, or artistic things. In sports, I have no problem finding something to be passionate with. In musics, I plan to learn one musical instrument before 30 yrs old. I will play the musical instrument, maybe violin, for my girlfriend:) That's how I am going to impress a girl..hahaha

My last hobby will be having my own garden and keeping exotic fish and a puppy. These will be done in Asia before I reach 30 yrs old!