Search assumes that you are able to describe what you're looking for, but that's not always the case. Browse gives you a set of cues about what's available and allows you to explore. Search gives you a big empty box to fill in. Browse is learnable, while search is, at best, guessable. Browse is transparent--you can observe how the links are organized. Search is opaque; the algorithms that determine your results are corporate secrets.
http://nform.com/blog/2011/08/three-problems-search-based-website-design
A thought provoking post describing some potential problems of building an organisation's website around a search interface. Particularly liked the simple explanation of the difference between search and browse
