The positive for the exchanges would be?
Well the exchanges like them, bots pay fees too.
Funny you mention this. Do you ever notice how may of those bot orders never go through? They are strictly there as false place holders and continue to change as the market changes and they cancel the orders and add them back in at a different price? So actually I would say on a percentage of traffic and stress on the system vs completed orders - bots are a complete nuisance to the exchanges.
That's a fair point. I have been visualising the live stream and often see bids/asks placed either side of the trade line, they appear as diagonal geometric patterns in the price/time domain comprising of many small orders. Obviously the bot creator is trying to make an analogue system from the disreet one. So some bots are quite spammy and will add to server load. I cant visualise cancel nor see the userid of the order creator, but I'm assuming many orders are cancelled as the bot tracks either side of the tradeline waiting for fast deviations.
The bot I am working on would not operate like this, it will place single well chosen bid/asks and of course cancel them instead of let them hang if the order is not fulfilled in time.
MtGox should perhaps consider limiting bid/ask orders that a user can place per hour or day. So bots would be allowed provided they didnt spam.