I was clearing out emails last week and found a load of receipts from a 'free' game i used to play.
started off playing for free > became impossible to keep up with the ones who paid for advantages
paid for a bit > then it became very hard to compete on a higher level with bot users - at the time though all the bots were being developed by small quite closed groups
helped with bot testing, took the piss in a big way, and got banned from every server i played on
once properly developed the bots become what people will pay for
Lots of money in 'free' games - whether it's direct to the game or outside of it to cheat.