Butterfly Bush Neglect

[Falls Harvest3]

My butterfly bush has been neglected for about 2-3 years has not once been cut back and is about 6'. I was woundering if the yellowing leaves on most of the branches and the dieing branches are because of this. Should I trim it back now to help it maybe? or should I just leave it alone until this fall?

[Evergreen]

Trim it back, but not more than one third of the leaves should be taken away, because the heat and sun can damage it.
The perfect time to trim that almost to the ground would be March.
It seems to have missed water for a few times...

[garden_mom]

My butterfly bush is about four or five years old, and last year it, and also my sister in law's bush of the same age, lost about three main limbs (or whatever you call them). Is this something we can expect every so often? Is it an age thing? Other than that, I only cut off dead material in the spring, or the occasional wayward new growth. It's now about 10 feet tall.