Why do you need to study phonology and speech arts?

Why do you need to study phonology and speech arts?
It is the study of how speech sounds are made. The International Phonetic Alphabet was designed primarily for studying speech to specify each sound that can be made orally to from words. All speech sounds are divided into categories, vowels which are divided into sub categories: front, central and back vowels depending on where in the mouth the sound is produced), consonants which are divided up into: sonorants, obstruents, fricatives, affricates, sibiliants, stridents, liquids,glides, and dipthongs. Knowing all these categories and their manner and placement of articulation can help further diagnose people with speech disorders.