A perfectly clear gutter can still be flooding your foundation

Gutters exist to move roof runoff away from the house, but that job isn't finished the second water exits the downspout — where it lands afterward matters just as much as whether it drained at all. A downspout with no extension just relocates the runoff a few feet, and the soil hugging the foundation ends up soaked every time it rains, even with a gutter that's completely clear and working perfectly.

Soil that's repeatedly saturated right against a foundation behaves differently than soil a few feet further out — it swells, drains, and settles on its own cycle, and over years that repeated wetting is a common contributor to slab and foundation soil movement. That's part of why most building codes call for downspouts to discharge water several feet away from the foundation rather than straight down at the wall.

It's an easy thing to miss on a walkthrough, because an unextended downspout still looks like it's doing its job — water is clearly coming out and draining. It's just landing in exactly the wrong spot.