Do debris cause rot?
When blocked, gutters will hold in all the water and debris, pinning it against the edge of the roof. That excessive moisture gets under the shingles and eaves, causing rotting beneath.
If you do nothing to prevent debris in your gutters then you’re allowing your roof line to catch all the pine needles, acorn, twig and leaf that falls off the surrounding trees.
It’s always best to have a gutter professional do the cleaning rather than attempting them yourself.