The couple of builds that for me found a use for focussed were purely shot speed decisions.
Foc 4 gives you 1610 which pretty much throws them through the same lead as multicanon.
General rule for me is to start with all efficient and then replace sequentially with s/r or o/c until it passes a management threshold..
On specialty builds you can play around with some fairly enjoyable combinations.
I use a super cold fas with two Sr c3 pa's and two c2 thermal vent beams.
So much fun in close.