I never let dead leaves lie. I rake them up ad stack them, though not on their own which would mean waiting at least two years for usable leaf mould. I stack the leaves with the abundant grass clippings that my large garden yields. That way, I get a really good compost in six months. Bob Flowerdew calls it accelerated leaf mould. I have access to abundant leaves and so much lawn clipping that it's my chief source of organic matter. Can't afford to be lazy in autumn - gotta get out there and rake up them leaves!