Remember that ab exercises alone will not give you abs! If you have the best abs in the world they will be completely invisible if you are overweight. Aerobic exercise and proper diet are even more important than ab exercises in getting that sought after 6-pack.
Form is very important in crunches, many people do them incorrectly and end up working out their neck or hips more than their abs. Use slow movements and only use the abs. Concentrate on trying to raise your shoulders straight up towards the ceiling. Don't worry about how many reps you do but focus on using perfect form. No whipping the head around or flapping your arms! This is not a sit-up either, the hips are stationary. Also important is to minimize any tension in the neck, I do this by very lightly supporting my head with my hands or the weight plate
The main reason to workout abs is because strong abs stabilize your lower back and shield you from injury but as a side benefit a 6-pack looks great!
Anyone can be healthier, have more energy, sleep better, and feel better about themselves through bodybuilding. Bodybuilding doesn't have to be expensive or take a lot of time, gyms are great but home workouts can save you time and money. A cheap dumbbell set from a garage sale or walmart is all it takes to get started with your home workouts.