How do you guys scale you campaigns? Horizontal or Vertical?
When exploitable scale it Vertical, way before you reach your vertical limit start looking for horizontal scaling and find out something else which can be taken to new heights. :-)
Figure out a vertical > Translate > scale to new geos its offered in. Cull the losers, scale the winners, work on losers if anything local/culturally can enhance ROI > once exhausted and team is managing dabble in new vertical rinse and repeat.
... easier said then done though :P haha - just always felt easier to scale what works horizontally before running across multiple verticals