Books have been set forth on this issue, and the debates and squabbling about where the "hot" slots are placed in the casino are still ongoing – over sixty yrs after the slot machines were first placed in gambling dens.
The classic rule is that the very best slot machines were installed just inside the door of the casino; so that people going by would be able to see real jackpot winners and be baited to come unto the gambling floor and play. Our disposition is that this is no longer the case.
Almost all of the mega casinos these days are giant complexes and you no longer can see inside from the sidewalk, so there’s no longer a reason to put the ‘loose’ slot games in close proximity to any doorways.
An additional traditional rule is that loose slot machine games are positioned on the major aisles in the casinos, again so that more potential players could see winning jackpots and be inspired 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 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 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 machines.