All matches is the standard search. The exact match requires that the full name match exactly, including both first and last names. However, the exact match does not need to be exact on search terms included in the second search box. The latter two categories start using fuzzy matches, where Gibson matches Johnson, Jane matches Janet, and Baker matches Barker, Becker, and Whitaker. While such search functions are interesting, it is only useful when you are not sure of the name of the person.
Most people trying to find an email address usually know the name of the person.
It would be interesting to know how many people find useful results in the possibly relevant set. Besides the tools mentioned previously, one longtime standard database to search is the Usenet addresses database. This database contains a clearly delimited subset of Internet email addresses. Thus, only people that have posted a message on Usenet news will be included in this database. While that by itself greatly narrows the scope of this database, remember that many email lists are mirrored on Usenet, so those addresses will be included as well.