Vantaggi
CSG was founded by a group of people interested in helping low income families with their heating bills. It has grown into a large, multi-hundred employee organization that is structured as a non-profit but runs like a company, getting effectively all its revenues from running utility and government energy efficiency programs. The culture is friendly and when I was leaving was beginning to strike a balance between the more mission focused folks who started the company and people coming from more traditional finance and real estate/construction industries.
My job was somewhat rare- most of the jobs are in the call centers and working on buildings or with contractors- either out assessing homes or training contractors that work on homes. There is a large marketing team that brands and markets the EE programs to utility customers and a business development team that bids on deals and would likely be some of the more interesting desk jobs for people who are not construction or customer service focused.
Svantaggi
It's hard to see what the career growth opportunities were. Jobs could be very specific. Compensation was also much more non-profit level than what you'd get working at some of the for-profit entities that do effectively the same work. That said, there were a number of people who moved through the ranks and clearly the culture wanted to nurture people who wanted to move up. I think it was more of a structural challenge. The HR person (who is still there) was a mover and shaker so I imagine there are much better structures for advancement and professional development now.