My own contribution is small but there is flexibility to shape outcomes and push for improvements to the user experience. The big picture contribution to society is large and it is rewarding seeing the software used to make governments and organizations more efficient. The opportunities for open data and citizen engagement are huge, and the public is getting more exposure as climate change, natural disasters, and epidemics drive a need for informational maps.
It is gratifying seeing the growth of awareness of GIS and geospatial tech, but I continue to believe it is wildly underutilized, and I try to contribute to changing that.
It helps that I can use the software in my free time and do really cool stuff with it. That and meeting customers at our annual events is deeply rewarding - we have really cool, awesome users.