I always see on movies people using Hand Chops. I know that this can be lethal to the neck, but does it serve any other purposes?
I've read that a chop to the throat can break the clavicle. If you break the clavicle, then if your attacker tries to swing a punch at you he won't be able to because the bone structure allowing him to will be broken. He'll also be in extreme pain as soon as he does. A chop to the throat, if done correctly, can also damage the throat but more importantly his ability to punch if done correctly. Though none of this is guaranteed so you should not rely on one strike to defeat your opponent.
You can also chop his temple. You have a lot of muscle on the side of your hand compared to your palm and the part that isn't muscle on that side is bone. I'm talking about the part of the side you chop with. So, if the first paragraph doesn't answer your question, maybe the second one does. It's most likely not as convenient to chop the temple as punching the temple, i.e. in boxing, but it will sometimes work. It's a lot more convenient to use the neck as your target in my view because you are more likely to hit the clavicle and you possibly could also knock them out there as well.
Hope it helps.
They've actually covered parts of this on the Skeptics SE. Short version, the reduced surface area of the chop lends itself to severely damaging the vertebrae and/or severing the spinal cord through impact. Within the movies, chops were used primarily because it was exotic-looking and it indicated a clear use of eastern martial arts compared to striking the person with a closed fist. In real life, it can be a dangerous move to do because, as mentioned in the other answers, it pits the relatively fragile bones of the phalanges against your target.
A chop to the neck can damage the blood vessels (e.g. carotid artery or jugular vein), the airway (e.g. trachea), or the cervical spine. A hit to the neck can also transmit kinetic energy into the spinal column. All of these are potentially lethal.
Strikes to the back of the neck, or at the base of the skull, are especially dangerous. The nearby tissue is responsible for many autonomic functions, including breathing. Damage there can be maiming or lethal. That's why there are no modern forms of sport combat that allow strikes to the back of the head (see e.g. Rule 15.A.xi. in the Unified Rules governing UFC and MMA).
As user2932 says, you can also break the clavicle (i.e. collarbone) at the top of the neck. As that's a structural support for the arms, that's a debilitating injury. It's also possibly fatal, e.g. in case of compound fracture.
The primary "non harmful" use that I know of for neck chops is the brachial stun: a chop to the side of the neck below the ear provides a several-second stunning effect, including pain and disorientation. A loss of sensation and control in the corresponding arm is also common. The attack is named for the brachial plexus, a network of nerve fibers that runs through the neck down to each arm. The vagus nerve also runs through that area; some sources cite it rather than the brachial plexus as the source of systemic disorientation. A number of "real world self defense" moves (e.g. "elbow entrance") and police and military fight training systems emphasize this kind of neck hit as a disorienting / stunning move. Given the proximity of the blood vessels, windpipe, and cervical structure, the brachial stun is still dangerous. There's no place you can hit on the neck that doesn't carry some risk of non-temporary damage and lethality.
(This answer portrays only to the majority of american karate businesses known as the infamous
It is my (bad) experience with karate where they teach alot of "theory" moves. That being, ones that sound good in theory, but would the actually work? most of these tend to be fake.
Of course, this doesn't apply to the (rare) good karate schools.
Anyway, a knife hand strike can be quite deadly. It depends on how you use it though. Of course, you wouldn't hit somebody on the top of the head like that, but a neck shot seems to be the best (and basically only). There is also another move where your standing to their side, and you do a low knife hand to the "peaches".
Like I said, a knife hand strike can be very powerful. My Sabomnim broke six large bricks with one these strikes, while I have broken 6 boards. Of course, this is on blocks. usually* an attacker will not be on blocks. There are exceptions, but I am yet to come across one yet...
If you strongly chop the throat hitting the adam's apple or even not, it might cause immediate but temporary asphyxiation or stun which will momentarily stop an opponent to fight. If you strongly chop at the side of the neck it might cause momentary stoppage on the opponent because the carotid arteries are smash and it may cause dysfunction on the flow of blood to the brain. At the nape a chop, may act like a smashing hard pipe, causing immediate death.