The arrows are indeed a debated effect, but many of us have noticed when you put a blue arrow on a back player, they suddenly decide to emulate Mats Hummels, and want to try to shoot.

I most often put the red arrows on my wingers, but it is worth playing around with them to see what works for your team.

The team cohesion thing, I think there might be something to that. New guys in my team usually take a few games to settle in.