Like your back muscles, your abdominals are quite important in stabilizing your body in all kinds of movements. The Abdominals you can train more than your back muscles, because it can be fatal if your back muscles gets to tired. Then they can´t absorbe different kinds of lifting, you may be doing in your daily life. It´s a little different with your abdominals they can handle more workout. But in general it is a good idea to exercise the opposite muscles in the same workout. For example your abs and back, biceps and triceps, front thigh and the back of your thigh etc.
Photograher: Christina Jensen, Strøby
This exercise I will call crossower or diagonal abdominal workout. The good thing about this exercise is that it also trains the oblique abdominal muscles. It additionally trains the straight abdominal muscles, hip flexor, shoulder and your motor skills.