What ever point you are trying to make is not coming out clearly. Perhaps reread what you wrote and you will see that it is not clear at all. Why do you think there are so many people that are getting on your back for what you are writing unless your intent is just to stir the pot which seems rather pointless to me. If you aren't interested in getting a better understanding of the conversation and what people are saying, why are you here ?
Your entire post is flame baiting.
I can at least attest to hitting a target is diffrent to air, i tend to over extend and cant properly strike without a target. hitting a target at least takes some of the issues out of it for me.
Have you ever been in a fight or full-speed/contact sparring match? Did you miss even once? If so, how did you handle that and why can that not be applied when not in a fight / match?
That said yes, it's very different. It's important to get time in hitting something with mass. It's critical feedback to your system (in the case of punching, we get feedback on wrist position, hand position, what sorts of strikes our hands can dish without immediate injury, etc). It gets you used to the feel of the shock that travels back. For small bags it helps with timing and aim.
You don't want the first time you kick something and meet resistance to fall over because you'd been balancing only for kicking at air. There's a dozen important reasons to train against mass; just like there's a dozen reasons to train against a resisting opponent. There's no single reason, and not everyone focuses on the same sub-set of reasons.
I don't agree about punching "through" the head, that's too far back. To me, punching has an optimal focusing distance, there is one point in the distance that you focus the power, power diminish before and after the focusing point. Focus behind the head meaning power is far from optimal when you make contact to the face of the opponent. The symptom of focusing too deep is the heavy bag swing back a lot when you hit as you are more pushing the bag than hitting the bag.
That's why when you look at people punching heavy bags, you can tell right away whether the person know how to punch or not. For people that know how to punch, you can see the heavy bag dent in at the point of impact. It will sound loud with a crisp popping sound and the bag vibrates but not moving back. That's a good punch......Good penetration, dissipate all the energy at the point of contact, no energy is wasted in pushing the bag back.
If this is not clear enough, look at a boxer punching heavy bag. I remember seeing a video of Joe Fraiser punching a leather heavy bag, you can see the deep indent at the point of contact and the bag didn't even move. That's transferring all the energy into a single point and dig deep into the bag.
I recall long ago when two guys came in with an interest in where I was training. Their background was pretty heavily boxing. One of the things we had in the school was designed for professional football teams. It was essentially a bag with a car spring in the middle except for the last 2ft or so which was a metal post that went into the ground. It was intended to be hit by someone practicing tackling (or whatever the word for linemen clashing is).
They hit it, it bent 5-degrees. I hit it, it bent more than 30. When I punched heavy hanging bags, I 'did it right" when they "jumped", sprining upwards as much as back from the recoil against the chain (depending on the hit). It's not an attempt at bragging... our goals were different so our approach/training was different, so our results were different.
Most accidental deaths in street fights (at least the ones I've seen make the news) occur when someone's head bounces off the ground or other hard object. As they say "the floor is the biggest fist in the room". So one reason for punching through is because knocking someone down is a useful thing.
But there's another basic reason... we tend to shorten our movements when under the effects of adrenaline. So wherever you are practicing to hit, expect that you'll extend less than that in reality (unless you are some sort of stone-cold fighter who just doesn't get nerves... well, or drunk). It's a result of the higher than normal tension that your body places on itself (you have muscles fighting your movement).
Also, I don't think people should rely on the bag to stop the punch, you contact, penetrate and you pull back. Or else in real fight, if the opponent dug and you miss, the punch will pull you off balance if there's nothing to stop you.
Agreed, and this was reasonably my initial point when I responded.
