Knowing the count is a key to having a feel for efficiency. The course distance is known so that dividing the distance by the stroke count yields the average advance of the shell per stroke. You can see that this would be a good thing to know. A large advance per stroke is an indication of efficient rigging and small blade slip in the water. A boat with smaller blades and awkward rigging would not advance as well.
Ideally, if the oarblades have no slip whatever (follow the zero-slip path), the shell advance is the greatest possible for the physical size of the rower. Size helps in this if it enables a rower to maximize the total arc of his blade sweep in the drive.
It would be a service to all, I think, if stroke count were included with the course distance and time in race results. Oarblade makers could then add stroke count and distance to their speed analyses of new designs.
* This per stroke distance count can be upset by both wind AND current so try to use good judgement. The error may be reduced somewhat if the data recorder accumulates distance run through the water or, simply, average water speed times course time although speed recorders based on rotating elements in the water can be in error by more than the small differences in performance sought.