A. If you are a successful trader and have sufficient capital, there is no reason in the world to join a firm (barring an invite to join a top hedge fund).
Keeping every dime you make while controlling all aspects of your trading decisions (or decisions not to trade).
There are advantages and disadvantages of trading for a bank. You are given monthly, yearly targets to meet.
Meet them and you get a bonus that is often very largely discretionary on the part of management. Fail to meet them, and your job can become imperiled…Not a healthy environment in which trade, especially when things are going poorly.
Working for a big fund that collects a 2% management fee and 20% of the profits? That’s pretty tasty…If you get THAT opportunity, take it.
As far as working with these firms in which you trade their capital, I have no experience with them whatsoever, so will not offer an opinion. Others out there may have a better feel for that arrangement than I.
Bottom line, trading for your own book can be the most rewarding, on many levels, if you have the ability to withstand losers as well as winners.