In 2013, I quit a 10-year job in the HFT/trading systems industry and went to work for small non-profit that developed web/mobile systems for humanitarian and human rights agencies. One of the best the things I ever did. What came out of it:

1. Completely upgraded my outdated skill set - from C++/Oracle to ES6/React/Redux/Node.js etc.

2. Completed a life-long dream of writing a full length science fiction novel (not yet published, sadly)

3. Developed computational psychology model (pet interest) that might one day be the basis of a paper

4. Learned proper leadership skills, public speaking skills and people management skills

5. Much better health - exercised, got plenty of leisure time (worked only 30hrs/week)

6. Networked through pro-bono consulting

It was financially punishing for me, but ultimately it was more than worth it. Last year I returned to the industry full time (a different industry this time). The additional skills/experience in the resume opened up a lot more higher level opportunities that I would never have been able to pursue 3 years ago. Right now I'm in a management level position doing exactly the kind of work I want to do, and I doubt if I'll ever have to worry about finding a job...

By the way, for anyone who asks, those 2 years were easily the happiest in my life.

Edit: cons: be ready to be poorer!