Pro-bono work can really get the ball rolling, especially when you're just starting out.
I never did pro-bono speaking but i did TONS of pro-bono training
I can think of two trainers in my area who started out doing almost completely pro-bono training, now both own gyms, drive expensive cars ( Dodge Viper, top of the line Mercedes Benze ) and make approx 10-20 times your average personal trainers income. They both pull in very high six figure incomes... all from what started as a pro-bono gig back when they were both broke a few years ago... I mean broke as in sleeping on a friends floor broke
I also started my biz doing a lot of pro-bono work. When I did it I got a TON of new paying clients from it... it works on many levels that are too in-depth to get into here
Heres a few blog posts about it... the first is about how I trained models pro-bono to position myself as an expert and the second is about pro-bono training in general.
Not trying to be too self-promoting here but I don't have time to type out how I did it all again so I'll just send you to my blog posts about it
The posts can be found here:
There Will Be Marketing
How To Build a Successful Health and Fitness Business Fast
Hope these help