This Is (A) Stupid Exercise

When you are working out, if you or your trainer have you do an exercise that makes you ask this question, then do question it! Even in Kung Fu training where we can come up with a lot of very original exercise we must be aware that many of these exercise might just be ineffective or, more importantly, possibly lead to injury.
One good way to determine if the exercise is good or safe is does it follow basic exercise guidelines. If it is a leg exercise, make sure that the knees don't go past your toes, your back can retain it's normal lordotic curve and does it really work the muscle that you THINK it works! A few good examples of this are 'plie' squats and kneeling kickbacks.
'Plie' squats are where you do a squat with your feet turned out as in ballet. These are supposed to work your inner thighs but do they? Your inner thighs are adductors (bring your legs closer together). In the plie squat you really don't bring your legs that much closer. Besides, your hips are in a contraindicated (putting you at increased risk of injury) position. Also, since many who do this exercise have the goal of teir inner thighs, why do one of the major muscle reducingbuilding exercises? There are far more effective and safer ways to work inner thighs. My favorite is to stand on a board or weight plae near a low cable pulley. Place the other ankle in an ankle strap with that side towards the pulley. Without holding on to anything, pull the cable towards you to bring your legs together. It is very challenging!
Kneeling Kickbacks are where you get on hands and knees and kick back with your foot. It isn't one that will really risk injury but if you aren't using any weight, are you really working? You could do over 100 of these and keep going. Yes, you would feel a 'burn' but that only means the muscle is using some fuel but not getting any stronger. The gluteus is one of the strongest muscles in your body. If you were to do a legs press you could do far more than your body weight. You would be far better suited to work your glutes muscles by doing lunges or split squats.
The next 'most abused' thing is balance balls and boards. Do these really improve your strength and balance. I have read far more evidence that they don't than they do. Here's one article:
http://media.cybexintl.com/cybexinstitute/research/Truth_on_Fit_March09.pdf
It reinforces what I am saying.
In conclusion, I almost always (I get 'fancy' when the person is a well trained client/athlete, they have no preconditions and I have assessed the exercise for effectiveness over risk) go for the KISS method of training- Keep It Simple Stupid. I know it gets boring but you won't have to go running to the doctor in two years with a chronic injury!