Maybe not you specifically, but the teams that are pulling in $1mm+ in fees.
I know several teams in NYC whose book of business is their own (especially those in tenant rep or IS) but stay at a firm that takes $350,000+ to print marketing materials and keep data subscriptions paid up. The few I've asked this question of say something to the effect of "ah too much work/paperwork to start it up." Doesn't seem that plausible for people who, in my experience, already work very hard.
Searched far and wide on WSO but doesn't seem to have been talked about. Perhaps a good discussion.