Extended range: The most obvious reason to use a 5-string bass is to access a wider range of notes. The additional low B string extends the bass's range down by a whole octave, providing access to notes that are not available on a 4-string bass. This makes the 5-string bass a good choice for soloing, playing in higher registers, or for adding depth and richness to the overall sound of the band.
Low-end support: The low B string on a 5-string bass can provide additional support for the low end of a band's sound. This is especially useful in genres such as heavy metal, rock, and funk, where a solid low end is essential for creating a powerful and driving sound.
Versatility: The 5-string bass is a versatile instrument that can be used in a variety of musical styles, from rock and pop to jazz, blues, and country. Its extended range and ability to provide a stronger low end make it a good choice for musicians who want an instrument that can cover a wide range of sounds and styles.
Orchestral and classical music: The 5-string bass is sometimes used in orchestral and classical music, particularly for Baroque, Renaissance, and contemporary pieces that require access to the lower notes of the bass range.
Personal preference: Ultimately, the decision of whether or not to use a 5-string bass is a personal one. Some players prefer the feel, sound, and versatility of a 5-string, while others prefer the simplicity and tradition of a 4-string. Whether or not you find a need for a 5-string bass in your music depends on your individual playing style and the music you make.