Eugene, OR
Blocked gutters spill water over the edge right where your siding meets your foundation -- exactly where you don't want standing water. Over time that means standing water and wet debris against your fascia boards, and water that never makes it to the downspouts pooling around the house instead.
Once water starts overflowing in one spot, debris tends to build up there fastest, which makes the next overflow worse -- the problem rarely stays the same size.
Clearing leaves, needles and moss debris so water reaches the downspouts again is a quick job -- most homes take about an hour.