Navigation serves visitors who do not yet know what they want; search serves visitors who do. A minority of traffic uses search, but that minority converts far above site average because searching declares intent. The two are complements — sites need navigation to be browsable and search to be answerable.
Navigation is a curated map: it teaches structure, communicates range, and works for exploratory visits. Search is a direct request: it assumes the visitor already has a target and wants the shortest path to it.
As catalogues and content libraries grow, navigation degrades — depth increases, categories overlap, and the map stops fitting in a menu. Search degrades far more slowly, which is why its share of successful sessions rises with site size.
Teams routinely conclude search is unimportant because few visitors use it. That reasoning is backwards. Search usage is heavily determined by discoverability of the search bar itself — an open field in the header attracts far more use than an icon that expands into one.
Search usage should be treated as a metric you can move, and the first lever is visibility, not relevance.