Whopity,
S-turns can be just as effective to lose altitude as a sideslip or flap. However, only for forced landing practice.
S-turns can be a bit dicey if you're on late final and trying to encourage the student to maintain a stabilised approach. Because they not only have to descend the aircraft back onto the normal glideslope but they now have to realign themselves with the RWY.
In mention of the original post, I too also agree with FormationFlyer.
If it's permitted in the Flight Manual go nuts.
If it's not permitted, then you're opening up a whole can of worms if you do it, even if you're more 'experienced types' say that it's fine.