All the rain from the gutters overflows from the roof down to your foundation. This standing water will crack your foundation.
Rainwater can rot the boards that your gutters are on, leading to leaks across your ceiling. Additionally, the water is pulled down your walls by gravity, leaving wet paths in its wake.
Rain gutters are meant to direct water, not hold it. When your gutters are tasked with holding rainwater and debris, they can be overwhelmed by the weight and break.