This is a really tough exercise that works your entire core plus several other secondary muscles such as your legs, arms and shoulders. (abmachinesguide.com)
This means a total core workout will strengthen not only your ab muscles, but many other secondary muscles which are crucial for proper posture, balance, stability and so on. (abmachinesguide.com)
Poor form reduces the effectiveness of any exercise (increases momentum, brings secondary muscles into play, etc.) and inevitably leads to injury and injury means less gains. (fitnessandpower.com)