These are very helpful aids for kicking and punching exercises. It makes a huge difference by the feeling of not holding back. (The pillow will give you feedback on how good your punch/kick is.) It will develop the feeling of hitting something. A good hit doesn’t stop at it’s ‘target’ but continues through it. 

But there is more to it. These kickpads come in handy:

• mark spots (like cornors of the mat during warming up; kids have to run outside it)
• you can make an ukemi over them, without being afraid of hitting them (this means you can stack them in height or in distance)
• use them instead of pawns (like in several fun-damentals)