Books have been written on this matter, and the contention and disagreement about where the "hot" slot machines are installed in the casino are still taking place – over 60 years after slot machine games were first placed in gambling houses.
The standard rule is that the best slot machines were placed just inside the main foyer of the casino; so that everyone walking by would be able to see real jackpot winners … be baited to come into the casino and play. Our frame of mind is that this is not so anymore.
Nearly all of the large casinos presently are huge complexes and it is not possible to see inside from the sidewalk, so there is no longer a reason to situate the ‘loose’ slot machines near any exits.
An additional standard rule is that loose slot games are located on the major aisles in the casinos, again so that more people could see winning jackpots and be motivated to play. Interestingly 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 slots 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!
Nowadays, casinos are constantly changing their perspective about where to place the loose one armed bandits.