On stringed instruments such as the violin, cello, and double bass, finger substitution is used for a variety of reasons.
In slow-moving music with expressive sustained bowed notes, finger substitution may be used so that a particular finger can be used for vibrato, to add emphasis to a note, or to introduce a subtle glissando effect (especially in Tango music and certain Romantic styles).
The bony side of the thumb cannot produce the same type of vibrato as the fleshy pads of a fingertip.
The technique is often used to create a connected, flowing legato phrasing, or smooth out sequence of consecutive thirds.
However, rapid or complex "pedal parts must be "choreographed" by the organist" and "carefully planned if they are to be successful".