If I do 200 kicks, next morning I'll feel tired. But if I only do 1000 punches, next morning I don't feel tired at all. It seems to me that the amount of energy that you may spend on kicking can be 3 times or even 5 times more that you do on punching. When you are young, you may not notice the difference. One day when you get old, you will feel big difference.
Also, only when you kick, you can realize your flexibility and balance. You don't need any stretching for punching. But you do need stretching for kicking. You don't need single leg balance for punching. You do need single leg balance for kicking.
Do you share the same experience? What's your opinion on this?