Video poker and slot machines generally pull in more than 70% of the average casino's revenues. However, the reason the casinos are able to offer these large jackpots is the odds on these machines that are some of the worst in the casino. Using computerized reels the odds are far from random and the casino is able to keep the inflow of cash constant.
Even those machines that don't appear overly digitized, have old fashioned appearing reels, and even pull handles, it will still be controlled by a computer. This is true for all the modern casinos, at least in the United States.
The thing that attracts people to the slot machines is the chance of winning a large amount of money for a small bet. Compare it to roulette, where even if you manage to get the number you bet on, you will at most win 36 times your original bet. At a slot machine, it is possible to bet dollars and win millions.
There are several disadvantages to playing slots despite the large payouts. It's hard to accurately judge the actual odds, although for the casino to stay profitable you would have to assume the actual odds are worse than the relative payouts. For example, on average, in order to get 100 times your bet, you will have to bet over 100 times, but you could say there's roughly a 50% chance you will only have to bet somewhere closer to 50 times as much.
You will want to find a lower minimum wage machine where you will be able to have what may seem to be an excessive amount of pulls available. If you realistically want to get the jackpot, you may be required to bet a decent chunk of it. You will also want to be able to buy all the lines on a multi-line machine for the best odds, which is generally required for the jackpot anyway.
The progressive jackpots are designed for groups of machines with a digital readout showing the increasing jackpot based on money paid into the machine. While they have much larger jackpots than the average machines, their payout rate can be as much as 7% lower than traditional machines. Therefore, you will want to find a machine where you are able to budget your money for a larger amount of sessions.
If the casino you play at offers a slot or comp bonus card, you should definitely use it. Even though the amount of cash you get back is generally small, the various comps, including free meals, buffets, and even rooms are something you don't want to turn down.
The common belief that these cards somehow keep track of your winnings or otherwise affect your chances of receiving a jackpot is completely bogus. The slot machines and the card reading system have no other interaction other than keeping track of the amount you play in order to offer comps and bonuses.