here is some info on bot trades from the ASX website:
http://asxnewbie.com/disadvantages-of-using-trading-bots/
One of the reasons they are used is to accumulate/sell a large parcel of shares over time without having too large of an impact on the share price.
If a broker is using bots to trade, I doubt they are incurring the same costs we do when we trade so I doubt it a factor for them.
