If by "perennial" you mean a plant which is going to die back to
ground level anyway, it doesn't much matter. It might not die right
at the hard frost (it might be sooner or later, depending on the
plant). But once it does, you can leave around the seed pods for
birds or if you like the look, or prune it. Either way is fine. This
is assuming the plant will be coming back from new shoots anyway.
Evergreens or woody shrubs/vines are a different matter. That one
depends on the plant a bit more, but many of them would not take well
to being pruned so drastically.
Then there are plants, like black eyed susan or evening primrose,
where the old flower stalk dies, but they have small green leaves all
winter. In those cases you can prune the flower stalk whenever it
dies but you leave the leaves.
I guess I keep thinking of special cases so I guess it kind of is "it
depends on the plant".
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