Does Focus adds to damage from elemental skills, such as the Berserker's Shadow Burst or Frost Breath?
If a skill says
deals X amount of Y as Ice/Fire/Poison/Shadow damage or just plain:
deals X amount of Ice/Fire/Poison/Shadow damage your Focus stat will be used in the calculation of your damage.
So if you're going to use a lot of skills that mention Elemental Damage, it makes sense to invest in the Focus stat. Even so, my Outlander uses only skills with elemental damage and only has Focus points invested.
It's also easy to verify this (if you don't mind using the console on a test character).
Frost Breath on the dummy, my level 2 hit for about
6 damage on average. I then gave him 200 more Focus (= 100% more elemental damage) and he hit for about
12 on average.