What are the unique characteristics and advantages of fretless instruments compared to their fretted counterparts?

Fretless instruments, like the fretless bass or violin, have a smooth fingerboard without frets, allowing for continuous pitch variation. This enables players to produce slides, glissandos, and microtonal nuances not possible on fretted instruments. Fretless instruments offer a more expressive and fluid playing style, but they require greater precision in intonation and technique.