I want to get this out of the way right in the beginning — if your idea of pro bono work is that you parachute in like a white knight for a few hours to “fight for justice” and fix the life of an eternally grateful client, please stop. It’s not like that, and you’ll just be disappointed.
Your client might hate you (or, at a minimum, blame you for only getting them 80% of what they wanted), justice might turn out to be a lot messier than you expected, and — I can pretty much guarantee this is the case — it’s all going to take a lot more time and effort than you anticipated.
That being said, it’s still one of the best things you can do. For the world, and for yourself.