Positive benefits: cleared my head about what I wanted to work on, what I wanted to avoid, and set up multiple long term relationships (friendships, spouse, etc). Took accelerate mandarin Chinese which was interesting but utterly futile when it came to use in my career.
Negative: my previous role evaporated at the end of 2000. I did absolutely nothing to set up my next job, because as a “highly valued employee” obviously it wouldn't be a problem (I was wrong). I didn't structure the time much at all, did not write the grand book I kept telling everyone I was going to write on the down time. Although my employer touted how wonderful its sabbatical/leave of absence program was, in practice I found it ended up being a negative mark against my employment history.
Regrets? I wish I'd planned it out a bit, and planned it for a full calendar year (at least through 2001). I should have lined up a role to return to before going on leave. The economy cratered while I was out and without a lock on a role I ended up in sort of a last-resorts role that I hated. I returned to work in a really bad month for my home city and dealt poorly with that trauma while diving into the world of a traveling consultant. I ended up leaving my employer after only three months back (for a startup, which was its own disaster).
I don't regret doing it? It's taken me some time to recognize how bad a spot I was in mentally at the end of 2000 and it was pure luck that I had the option to go on leave. I did not appreciate that the combination of returning from a foreign assignment in 2000 with a sabbatical in 2001 would leave me with a really weak internal network to find a new role.
A previous comment I wrote about this: https://news.ycombinator.com/item?id=27238018