How important are obliques to obtaining good ab muscles?

I'm a bit of a strange case, I naturally have next to no muscles at all. What many get just from genes I had to work out for months to acheive.

Anyways, now that's out of the way I understand good definition is all about being cut, but in the development of good abdominal muscles, I was just wondering how important the obliques are.

When I first started working out I used to exercise them, but for some reason I stopped, (can't remember why). I just need to know if it's worth my workout time to do some side planks or if I should concentrate elsewhere.
 
direct quote from Chillen's website (way down at the bottom):

EXERCISE AND PERFORMANCE TRAINING TIPS
In designing an abdominal workout, choose between 5 to 10 exercises, combining spinal flexion, rotation, and lateral flexion exercises. Perform 8 repetitions of each exercise before going on to the next exercise. Every 2-3 weeks, you are advised to vary your workout (refer above for ways in which to vary your program). Strive for quality of movement with each contraction. Also, visualize your abdominal muscles contracting tighter with each exercise, stressing the importance of the contraction. Although it’s great to do these exercises with accompanying music, try not to let the music dictate the tempo of the exercise. Slow and controlled movement is always best. During all exercises for which you need to support your head, do so in a comfortable manner that does not allow you to force your chin towards your chest.
Although the abdominals are a troublesome spot for many people, the knowledge and tools you now have, will, with hope, highlight your abdominal exercise workout, while helping you achieve your health and fitness goals.
 
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