In the case of complex queries, the capability for specifying search parameters in detail becomes important. If the search engine retrieves documents containing any of the search terms, this is a different thing from retrieving documents which contain all of the terms, especially if relevance is based on a straight count of occurrences. Most search engines usually allow you to specify how search terms are combined, either by typing the search string using the Boolean terms AND, OR and NOT into the search window, or giving equivalent functionality via drop-down menus. Words that must be in the document can often be indicated with a plus sign, and those to be excluded by a minus sign. For example, a search for anthropologist is interpreted as a search for anthropolog.
Some search services interpret adjacent search terms starting with capital letters as proper names.
Frequently it is a significant factor. Many search engines provide this feature. Most search engines take some portion of the text to provide an abstract. Dates are often useful. A number of search engines give the option of treating all pages from one site as one entry, a feature which is often useful.