The more playing around with arrows I do the less I want to use them without great thought and reason. I have no evidence (who does) but I find arrows can break a teams prospects as much as it can boost them. I use them as an extra tweak. And I find I'm using them to do things not covered by other aspects of a set up eg leave attacking down the flanks wingers without arrows and instead arrowing a central midfield to support them.

Remember players are hardly ever in the positions you assign them at the start.