Overheadcosts on distributed still image renderjobs
Distributed renderjobs do usually cost about 3-4 renderpoints more than single node renderjobs.
The technical reason for this is the scene preparation time, which counts as rendertime.
That preparation occurs at least a 100 times, instead of just 1 time on a single node renderjob.
(also depending on renderpasses of a job).
By lowering the number of nodes, you can achieve slightly lower rendercosts,
since the overall preparation times get reduced.
This is especially an advantage on short rendering still images (less than 5 hours e.g.)
since an overhead of 3 renderpoints (rp) on a 50 rp job won't be that crucial different, than on a 2 rp job.
Please note that the job will take longer to finish, since less nodes are assigned.