What is known in dance terms as ‘spacing’, doesn't have to be a deliberate decision made by the choreographer. It can be treated as  an emerging constellation managed by the dancers in relation to the work being done and the task at hand. In most cases, making an active descision such as upstage/downstage, right/left etc, will result in a simplistic, non organic and not very credible result. Spacing at its best, simply happens. Trying to pre-organise this, will get in the way of the naturaly emerging spatial relations between the dancers. There is no sense of randomness about this, it is actually allowing a deep logic of organisation to take place. There is a phase along the process though, when actively making decisions in relation to spacing, becomes relevant again as a creative tool. But i find that most times it's happening quit late in the process. The more you wait, the more things will tend to "fall into place" with a logic that is impossible to reproduce artificially. it is impossible to try and recreate the complexity/richness/coherence of self governed choreographies. In that sense, a horizontal system, devoid of hierarchies, will always be more artistically efficient and reviling than a vertical, hierarchical one. Spacing in that sense, is a group endeavor rather than one managed by the choreographer.  
And also, the right spacing is always the result of precise, clear musicality.