To get all the benefits of it, combine it with other core exercises as a part of a consistent training regimen. (fitnessandpower.com)
If you have poor core strength, poor flexibility, lower back pain, or have poor overall fitness, I recommend that you use other core exercises in your routine. (ab-core-and-stomach-exercises.com)
Plus, not everyone likes doing crunches, like me, and you can choose from a lot of other core exercises that are more enjoyable, burn more belly fat and engages your core muscles more efficiently. (abmachinesguide.com)