Legal periodical indexes generally only allow you to search the title, citation, abstract, keywords (sometimes author-supplied), and subject terms given to a journal article, rather than the full text. A benefit to using a legal periodical index is that it will include all issues and volumes of a given journal, without any gaps in coverage, back to a certain date. (For example, Legaltrac's contents go back to 1980. Full-text databases can have gaps in coverage--sometimes many years' worth for an individual journal.
If you merely use "AND" to connect your terms, they may be located at the beginning and end of your result, and may have little or no relevance to what you are really looking for. (AND is what is usually used to connect terms on web search engines like Google or Bing.)