The built in thesaurus and "any word forms" together will give a very broad range of matches, where words derived from the same root may be found, even if the meaning has since diverged a bit. What the right answer is depends on the goals of the searcher. The builtin thesaurus and all word forms may be most appropriate for a researcher making sure they don't miss anything, and seeing related concepts that may not immediately be obvious is helpuful.
It may be for example having a more restrictive thesaurus, where for example abstinence and temperance are the only synonyms for sobriety, or having a step allowing the thesaurus and just plurals and possessives, or a more restrictive custom stemming list first.
It may be for example having a more restrictive thesaurus, where for example abstinence and temperance are the only synonyms for sobriety, or having a step allowing the thesaurus and just plurals and possessives, or a more restrictive custom stemming list first.