The torso rotation machine works, as long as you're using it properly to target your obliques. It works the serratus (internal obliques), which extends from the side of the abs to the lats at an upward angle, covering the ribs. For bodybuilding purposes, it adds a lot of definition to the midsection and complements your abs really well. For functional purposes, it helps supports your spine and is the primary muscle for rotating your torso, so you can turn to someone to the side without moving from your chair. For sports, it is an important muscle, especially for when you're throwing with one hand (baseball, American football), swinging objects (hockey, golf, tennis, baseball), etc. It is part of the group of core muscles in the body.