You see the tube in the center of the toilet tank? That is the overflow. If the float fails and water continues to pour into the tank the excess watet flows down into the bowl.
A client called us because he kept finding pools of water on his bathroom floor.
We discovered that the float was jamming and the excess water began flowing onto the floor.
But wait. What about the overflow?
It is difficult to notice in the picture but the overflow tube extends beyond the two holes on the sides! The cap on the left and float on the right are not water tight.
We have seen this several times. Go check the toilets in your house and make sure the overflow is installed correctly.