I was really dissatisfied with life a few years back, so I took a year off work and lived off my savings. I attributed my dissatisfaction to work and I basically said to my boss I needed to do something else for a while, and I'd come back in a year if they'd have me.
I had a decent bunch of savings and nobody to support, so I could afford to gamble this way. But they did take me back.
I had a bunch of ideas beforehand about what I wanted to do, projects and so on, and many thoughts about what I was fed up with at work and a feeling I needed more time for my own projects. I tested these notions and ended up realizing that I was mostly wrong in my analysis.
I thought I wanted was more time to decide what I wanted to do with, to hack on projects, but in the end what I realized I lacked was variety in life.
So since then I picked up a bunch of new hobbies. Like in the years since I've dabbled in everything from partner dancing to latin. I'm a lot more well rounded now and I'm a lot happier for it.
I've also worked 32 week hours since then to have some more time for other stuff. Well worth the pay cut.
In the end, I never really accomplished very much on my sabbatical, but I did come back a much more well rounded and happy person. It's probably a far better tool for personal growth than it is for productivity or career advancement.