Span of control captures a basic structural choice: how wide or narrow each manager's team is. Wide spans, with many direct reports, tend to flatten the organization and push autonomy down. Narrow spans add layers and tighten oversight.
Neither is right in the abstract. The appropriate span depends on the work: routine, similar tasks support wide spans, while complex, varied, or high-risk work usually needs closer management and therefore narrower ones.
Span of control also drives cost and speed. Every added layer adds coordination overhead and lengthens the path a decision travels, which is why it is a recurring lever in operating-model and organizational redesign.