Books have been said on this matter, and the controversy and ruckus about where the "hot" slots are located in the casino are still on-going – over sixty yrs after the slot machines were first placed in the casinos.
The standard rule is that the most favorable one armed bandits were put just inside the entrance of the casino; so that folks walking by would see real jackpot winners … be possessed to come unto the gaming floor and play. Our assessment is that this is no longer true.
Nearly all of the major casinos today are herculean complexes and it is not possible to see inside from the sidewalk, so there’s no longer a reason to put the ‘loose’ slots close to any exits.
An additional standard rule is that loose slot machines are located on the major aisles in the casinos, again so that more people could see winning jackpots and be inspired to play. Notably though, we find that this also isn’t a universal rule any more.
What casinos found over the years is that people walking down the busy aisles were frequently on the way to somewhere else. If they played the slot machines at all, they would simply put in their loose change because they happened to be walking by. Win or lose, they would very often not stop to keep playing. And the very last thing a casino wants is for someone to win a jackpot by playing only a few coins and then not stay to put it all back in!
Today, casinos are constantly changing their philosophy about where to place the loose slot machine games.