Deadhead Perennials in Fall?

I'm not sure whether or not to deadhead some of my perennials now that it's fall (zone 6). Specifically: liatris, agastache, boltonia, black eyed susan, coreopsis, phlox, and butterfly weed. (somehow, the baptisia doesn't look like it should be cut back--I guess because its leaves are green, not brown and dried.) Can anyone advise?

I always like to cut my perennials down to a nice 4" height. Now that is a general thing, of course. This advice would fit for all but the Agastache and I have no experience with the boltonia or baptisia. The Agastache should be cut so that 8-12" remain standing.

I cut all my perennials down after killing frost to ground level. Plants have no use for stems when they go dormant, plus they will kill back anyway with winter. It is also easier to cut back in the fall while stems are still soft. Also stems left standing can harbor insects. It is easier to rake up leaves if you don't have to fight stems.

I am too busy in the Spring so cleaning up in the Fall saves me time. A weed eater will come in handy to trim back stems. Blooming stems grow from the soil on most plants. The exception are irises. Their fans I trim back to 4".

My daughter grows Agastache and she trims hers way back.

On the other hand, leaving plants standing during the winter has its merits too. It creates some winter interest, the stems trap and hold snow, and birds and other animals can feed on the seeds and stems. Other than some possible advantage from holding snow (depending on your thinking about that), it makes no difference to the plants - the stems are (mostly) dead anyway.

Thank you all for your sensible advice. Much appreciated.

I mostly do it the way altagardener mentions, I like to allow all the sap from the stems to be taken back down to the plants underground storage as it helps offer feed for the following spring where they have to use up energy to make even larger clumps and roots.
Any fallen or diseased parts are removed but the best use of the dying / dead foliage is it offers protection from snow / frost and even acts like a blanket on the soil.
I dont find it difficult at all to remove the dead / dried top growth, it normally just gets a gwentle tug for it to be removed without damage being done, but always check as sometimes new little green shoots come away with a old dried part and by removing the dead area, you can replant the little off cut to give a new plant with less trouble that germination of seeds.
The birds AND insects will love your garden IF you leave the spent flower-heads, hollow stems etc as these are winters hibernating spots for all different types of insects that help keep our plants healthy, pollinated and will come back to your garden year after year once you build us a natural haven offering protection. Remember ALL insects are not our enemy.
Best Wishes.
WeeNel.

I leave some (Echinacea and Liatris) flower stalks up for the birds to eat during winter.

I agree with WeeNel. I leave cleanup until Spring. We have many small birds around here that eat some of the seeds left in the dry/dead flower heads over the winter.