IPA transcription is integral for academic fields that conduct language research, including linguistics, speech-language pathology and second language acquisition. IPA provides researchers with a common language in which to communicate specific articulatory correlates. Writing systems of different languages do not have a one to one correlation of sound to symbol, and using a regular alphabet system does not provide a level of phonetic detail that is the subject of many researchers' work. IPA provides researchers with a way to distinguish the Korean "b" from the English "b" from the Spanish "b."
Speech-language pathologists (SLPs) commonly use IPA to record an exact description of a particular utterance. There are many supra-segmental components of language and articulation that cannot be captured using the English alphabet. These components include pitch, intonation and speaker intention. SLPs can use IPA to distinguish when a child is correctly voicing a sound and when she is not. SLPs also use IPA to collect data on articulatory patterns of their clients. Through the detailed transcription of a language sample, an SLP can detect patterns in the clients' speech that may need remediation.
Perhaps one of the most underused aspects of IPA is as a tool for second language learning. While it can seem daunting to learn a new alphabet for the purpose of learning a new language, the payoff in accurate pronunciation can make IPA expertise worth the trouble. Mandarin Chinese is considered one of the most difficult languages for native English speakers to learn because Mandarin has a variety of retroflex consonants (sounds articulated with the tongue curled backwards) not present in English, along with the supra-segmental tonal contrasts. However, if you study IPA and gain an understanding of the different places and manners of articulation, you can practice accurately articulating Mandarin sounds based on the IPA parameters.
IPA does not have to be used only for serious educational pursuits. Once you become proficient in writing in IPA, you can used it for your amusement instead of just for science. Print a T-shirt with a saying written in IPA to identify other language nerds, or write a note in secret code to friends who also know IPA. You can even practice transcribing your favorite songs in IPA and then perform IPA karaoke.