i'm afraid this is a complete misconception of rope jumping. so how would you get someone into good shape prior to tournaments or just globaly speaking? jumping rope is an exercise that requires small but explosive moves, wich makes it REALLY HARD to get injured. you'll probably get injured more easily walking down a stair.
of course, we're not professional rope jumpers so yes of course it's just additional form of training, you're all badminton players afterall (so am i but now just for recreation and stamina),but that doesn't mean that people shouldn't jump rope. there are no negative sides of rope jumping, it can only benefit you.
for you who play badminton, tempo is crucial, if your legs can't keep up the pace in later stages of game, you're most likely to lose. RJ makes you keep the tempo up all the time, it increases both your aerobic and anaerobic capacity. if you pick up the pace to about 2 turns per second, it can make you go up to 85-95% of your maximum heart beat rate. for badminton crucial, it develops your fast twitch muscles. it develops your balance and coordination (again very important for badminton), agility in most effective way, speed, quickness, explosivness, you name it bro. and it's not just about your legs, it will hit your whole upper body muscles, chest, traps, back muscles, shoulders, and not to mention your forearms and wrists. when you pick up the tempo your forearms shall cry, of course until you get into better shape. RJ is also a mental training because it improves your concentration, until you try jumping you won't know how important factor this is.
a long time ago i've found a very nice exercise comparison chart saying:
10 min. RJ at 120 turns/min produces the same cardiovascular fitness as: two tennis sets, 20 min. handball, 30 min. jogging, 12 min. swimming, running 1 mile in 12 min., cycling 2 miles in 6 minutes.
so i really don't see what's so wrong with spending some time that was anyway booked for conditioning on rope jumping.
my current training partner thought that jumping rope was just for little girls hopping down the street, but i can tell you that he changed his mind after the first few minutes of jumping.
now...go buy some ropes ppl