One other, minor factor, is having them facing inward or outward can stiffen or loosen the axle. It’s a very minor tuning aid, and I haven’t met a driver yet that could feel the difference, but it will change the axle’s deflection.
Facing in will stiffen the axle a tad compared to facing out which loosens the axle.
Just an update to this, I was speaking with someone who’s been using these for quite a while and he said to ensure both collets point in the same direction. Since the collars pull the axle during tightening, having the collars pointing inward would cause a lateral tension and the collars both outward would cause a lateral stretch. Having them both in the same direction will also cause the axle to shift 1mm in that direction after tightening the collars.
If there are any racerz here that believe they can notice this, or have this effect their lap times by any measurable amount, Torro Rosso has a car with your name on it!