ðɪs ɪz dˈʌn fɚɹə vɚɹˈaɪəɾi ʌv ɹˈiːzənz sˈʌtʃ ɐz ʃˈoʊɪŋ mˈoːɹ diːtˈeɪl ɔːɹ hˈaɪlaɪɾɪŋ sˈɜːʔn̩ ˈæspɛkts əvə fˈʌŋkʃən, lˈaɪk lˈɛvəl sˈɛts.
This is done for a variety of reasons such as showing more detail or highlighting certain aspects of a function, like level sets.