I cut nearly everything back in fall. I do this because it is convenient for me. In spring, I have way too much going on, 100s of other chores in the garden, and I don't want to have to worry about pulling wet slimy dead perennial leaves as well.

There are some I leave, such as my fall-blooming anemones, which have iffy hardiness. Sometimes I'll leave fall-planted perennials, just for that little extra bit of insulation from their foliage.

I've read that you only cut the green stuff back after it has died. I imagine that it's so the plant can continue to get as much sun as possible for as long as possible. I imagine that it feeds the plant until the last possible moment. I could be wrong but that's the scenario I've worked out in my little brain. That said, my mother has a GLORIOUS garden in Bangor and the week she told me she cut everything back (about mid october) - I cut all mine back too. If she has success year after year then why not.

Are you cutting back spent perennials or shrubs? Shrubs may require different handling. Depending on when they bloom. Spring, summer or fall blooming shrubs-each have different needs.