Clogged gutters overflow, sending water down your walls, into your foundation, and behind your fascia where it rots wood. Cleaning them is one of the highest-value maintenance tasks for preventing water damage.
Clean safely
Use a stable ladder on firm ground with someone holding it, or hire out the job if you're not comfortable at height. Scoop debris into a bucket, then flush the gutters and downspouts with a hose to confirm they drain.
Check the downspouts
Make sure downspouts are clear and that water discharges well away from the foundation — extensions help. A clear gutter that dumps right next to the house still causes basement problems.
How often
Clean at least twice a year — spring and after the leaves drop in fall — and more often if you have overhanging trees. Gutter guards reduce, but don't eliminate, the need to clean.