If there is sufficient quantity of any organic material on a roof, especially in a valley area, then the organic material will remain wetter for an extended period of time and thus, also allow a possible expolsive growth of licen or roof algae to set root into the organic shingle roofing materials.
Once a cluster roots, grows to a sufficiet size and then detaches from the roof, it can or usually will remove the associated shingle granules off of the surface of the shingle, therby leaving a bare asphalt spot at each location, which therefor will allow the exposed asphalt to degrade prematurely from the direct affects of the harmful rays of the UV Rays of the Sun.
If they are just small deposits, which blow around on and off od the roof when the wind blows them around and they are dried out, there should be no such adverse problems associated with the fallout.
Actually, the more times that you walk on the roof shingles, with improper walking motions, you can scuff and damage the shingle surface much quicker that what the pine needles could possibly do.
I would recommend a leaf blower for you to use, aiming from top to bottom, as long as the slope of the roof is safe to walk on and you have the confidence to do so.
Ed