What is their role? Afaict they seek to gain banks & hedge funds as clients to trade with them as a kind of middleman, instead of trading directly at the exchange, for "liquidity" reasons. (i.e. not impacting the market with whale orders? Is there another reason?) How much do these people make (in NY and in London)? Seems like it is a whole lot easier to get in than as a trader, quant or engineer.