Years ago I read to not prune butterfly bushes & Russian sage until there was growth on them. Maybe that was the wrong advice, but my butterfly bushes & RS has always done well. I get lots of blooms, at least compared to the years that I couldn't prune at all. I don't tend to prune quite as hard as you do, back to 12" or so, but I don't think it would make any difference.

Yes pruning your butterfly bushes as soon as you can will benefit them.

one might argue.. that it has wasted some level of energy ... but who cares ...

rarely do things die, due to pruning ... worst that can happen ... is it loses a year.. while regrowing ...

and if it does die.. there was probably other problems ...

ken

Prune the Buddlejas now. They bud here almost as soon as the leaves fall so there is barely ever any time when the branches are bare. They'll come to no harm.

Yes, prune them. I cut mine almost down to the ground, they grow like weeds and will fill in quickly once growth begins.