My yard is full of pollinators and small living creatures of all sorts. For years I did full fall cleanups (ok, my yard guys did full fall cleanups) without fail. I didn’t have very many little beings in my yard. Oh, some, like everyone else, and of course I have been raising Monarchs like mad for years.
But one year I was so frustrated that I couldn’t get the guys to stop chopping 
down and taking away my milkweed seeds before they were ready for harvest that I told them not to clear out any of the milkweed beds. Wow. The next year, we had so many wonderful beings! Moths I’d never seen before, bees of all kinds, and fireflies… so, so many beautiful fireflies.
This article in the Chicago Trib by the director of horticulture at the Botanic Garden explains it well: http://digitaledition.chicagotribune.com/infinity/article_share.aspx?guid=e2140e76-a4cf-439a-a0ad-3854faedb09e
So glad to be one of the cool kids who leaves my leaves and shows my pollinators some love!!