The reason for these larger "trench drainboxes" is two-fold. The first is that the drainage box of the trench drain allows capturing and channelling of more water. With global warming, there has been an increased amount of strong precipitation from year-to-year requiring more management of runoff rainwater. Should your box be too small or the drainbox cover be covered? The rush of water can flow over the drainage box and creep between the concrete sill and the garage door seal causing unwanted flooding in your garage. The deeper box of a trench drain captures the excess water and properly directs the flow of water into your drainage pipe, then into your garage pit, and out the storm drain. The large "drainage grate" will decrease the likelihood of the drainbox being blocked by falling leaves and debris in the fall.