Branch Out drains always power

That's a facepunch thing unfortunately and is less of a bug and more just a choice on their part. Branches have one task, branch off power, whether that power gets used or not isn't up to it.  
Makes it a bit pointless to try to be efficient for car lifts with switches or HBHF sensors because it just results in using even more power.

IIRC, though, it does mean that you can use that feature to fine-tune your daylight sensors so that your lights come on earlier and go off later.