That coin chute is the overflow. When the hopper gets to a certain weight (you can set it) it "leans" on a switch that activates a diverter, directing the money down to a bucket below in the (locked) stand. If you look at where the coins drop in, inside the door, you should see the diverter coil. There's also a lockout behind the coin mechanism. That engages when the highest amount of coins are inserted, usually 1 - 5 depending on the machine. I can't quite see yours... the photo is too small - 3 maybe? When the lockout engages, any additional coins inserted will simply fall in the tray.
In the casino the "drop money" that is diverted into the bottom drop hole is collected late at night in a ritual called "the drop" and is operated by the "drop team" who are escorted by a team of security guards.
The drop money is counted and that is the profit for the casino. Those coins are rolled up to produce rolls of quarters and nickles which are taken to the change booth and sold to the casino customer
to play in the games.
The money that is vended and falls into the hopper is kept there and is not considered casino profit, it is called the "players money". If the hopper is too full the weight of the excess coins tilts a "weight switch" on the hopper and opens the diverter flap to allow the coins to fall into the drop.