Okay, your standard lottery game has a fixed number of possibilites. So, buying every single possible combination, while difficult and time consuming its quite possible. Now lets make this into a nice formula:

Profit = Winnings - Number of Tickets/Combinations x 1 Dollar

So if there are say 10 million possible combinations, and the payout is say 50 million, you'd be crazy not to do this. Granted it does have some problems, if more than one person gets the right number you have to split the money, so thats always a consideration. This particular scheme though, probably won't make you very popular with your Lottery Commision. I remember seeing this put to work on a TV show once, I think it was bunch of Australians (In New York) who did it, they got a couple of investors to help buy all the tickets, and used computers to generate the ticket slips and bought them at a convience store for some reason. Unfortunately the store stopped accepting them after a point, so they had a large gap of numbers. They won anyways though.