The way my instructor puts it is simple:
Anyone can punch or kick, this is about learning to TAKE a punch and a kick. We take care of each other, we aren't out to break anyone, but, contact is a vital part. It isn't enough to punch the air. A bad attacker in class won't help you learn. If the punch isn't going to hit you, you don't need to block it. A realistically thrown punch or kick makes it a hell of a lot easier to execute properly.
Anyone can punch or kick, this is about learning to TAKE a punch and a kick. We take care of each other, we aren't out to break anyone, but, contact is a vital part. It isn't enough to punch the air. A bad attacker in class won't help you learn. If the punch isn't going to hit you, you don't need to block it. A realistically thrown punch or kick makes it a hell of a lot easier to execute properly.