Both are useful, but cover slightly different aspects of the field. One would have to evaluate them for relevance to a given need. My goal here is not to imply that relevance is a matter of semantics or depends on context. Rather, it is to emphasize that relevance is an important concept to apply at various stages of information gathering. And in the evaluation stage, one must determine the pertinence and relevance of items retrieved.
Relevance is an integral part of searching, especially on the Internet.