I'd figure safety, particularly personal safety, was everyone's primary concern. Personally I've taken a different spproach than most by opting for WIDE light coverage front and back, and have found that literally painting the road red behind me by pointing the rear lights downwards actually gives motorists the most effective (visible) announcement that I'm there, without ruining their night vision.

Mounting the lights strategically can also light up part of the front and rear wheels with side spill, and I think that could be made even
ore effective with the addition of reflective tapes. IMO that just optimizes available light in a manner that more clearly identifies me as a cyclist to people not directly behind or in front of me - hence promotes safety.