It depends on the pricing deal that is set up between the trader and the prop firm (per-share, per-execution, per-order, pass-thrus, all-in, etc.)
Assuming that the ECN, SOES, SDOT, and SEC fees are passed-thru to the trader, the only revenue earned by the firm is the mark-up they put on the per-share or per-execution/order rates. In this situation, they would be more inclined to have the trader trade more volume.
However, it makes no sense for the prop form to have a trader blow out his account with fees/losses since this revenue stream would dry up if the trader left. It isn't that easy to keep bringing in traders willing to fork over $5k-$10k on a steady basis.
If the prop firm gets a percentage of a traders net P&L (20-30%) then they would prefer to have a profitable trader as opposed to just a churning machine since this % of profit can be lucrative.
A prop fims perfect situation is one in which they have a trader who writes a ton of tickets and is profitable (where they get a % of the profit). However, they can't just push a novice trader into a high volume trading system they are unfamiliar with and expect to be able to sustain a business (unless they are great at bringing in new $5k-$10k donations)
