Definitely not true. It really depends on the hose that is cracked. A cracked vacuum hose that causes a vacuum leak will definitely create a problem. A cracked heater hose will most likely cause a water leak and your car will overheat when you end up dumping all of your fluid. BUT, a crack in a breather hose, which connects to the intake BEFORE the throttlebody will not cause any problems. This is the hose which is shown in the pictures above. A crack in this hose will cause the breather gasses (air + oil-vapor) to escape into the air, and thus create a neglegent increase in polution. It will not create a vacuum leak because it connects to the intake BEFORE the throttlebody, nor will it create any other performance problems. A crack in almost any hose will create problems, a crack in this hose will not.