Calling this method set the match mode to exact matching. By default the match mode is set to inexact match mode. When in exact match mode terms must match exactly (after the character map is applied) for the thesaurus match and any associated weighting or penalty to be applied. In the default inexact mode a match will be applied even if the term in the query or record is slightly different than the term in the thesaurus. The amount of difference allowed between the thesaurus term and the term in the query or record is determined by the length of the term, short terms must match exactly, longer terms allow one or two character differences.

One place where exact mode by be approriate is when you have terms in your thesaurus that are very similar but must not be confused.