There are other reasons of having exercised abdominal muscles than just having six pack abs.
Strong abs also help your back muscles and your posture.
So not all reasons are visual.
Having a good balance between your ab muscles and back muscles can prevent a back injury later in your life.
Stronger abdominal muscles and core means that you have more power to use in anything where stability is needed, like sports or other daily activities.
Firmer abdominal muscles will make your stomach a little leaner, but just doing them you can't achieve miracles.
So if you are trying to really get a flatter stomach, you need to look at what you are eating.
A good diet is the most important thing what comes into shaping ones stomach.
Exercises definitely have their place, but exercises alone don't get you a flat stomach if you have a good amount of fat around your belly.
How should you exercise your abs then? Most common mistake is to do way too many repetition in your sets.
The truth is that you should treat your abs as any other muscle in your body, exercise it 3 - 4 times a week and to do 20 - 25 repetition sets if you want to get your stomach leaner.
Cardio exercising should not be forgotten, high intensity exercising might be the easiest way to burn fat.
This means that your cardio exercise take at the most 40 minutes of your time, but still results will be good, yet the exercise itself will be really hard.
Doing ab exercises is definitely a thing you should do, not just for your looks but for your overall health.
Exercising overall is recommended and just doing various ab exercises will get you just strong abs but your back muscles and other muscles will stay weak.
So exercise hard and exercise overall.