When a person types, it can often be difficult to find the correct spelling for words that sounds in one way but are spelled in another. For example, words "I" (as in me) and "Eye" (used to see with) is pronounced the same way - but spelled totally different. To find the correct match in these cases, the search feature must handle a phonetic match, not just a traditional spellcheck. Otherwise it will surely miss matches that the user might be searching for.
When you include techniques for a phonetic search inside your search feature, the visitor/customer/user can type the words as they sound, without bothering about spelling them correct. The search will match on everything that sounds correct, regardless of how it's spelled. Phonetic search at it's best!