Kickboxing and Boxing students often use blocks to defend against strikes.
Blocking is the least effective form of defense.
First off, throwing your forearm out to meet force with force in order to stop it causes you to draw your hands away from your head and torso.
As well, since you are trying to halt the attack by throwing your forearm into his forearm, there is a strong likelihood that you’ll bruise or injure yourself as you attempt the block.
Now, in Boxing, blocking does work and it is natural to do (every person I’ve ever taught how to fight blocks to defend punches).
Unfortunately though, it opens you up for fakes and combination attacks. Due to the distance you create between your hands and your head, you’ll never be able to get your hands back fast enough if he launches subsequent attacks to your face.
Blocks should only be done as a last resort and if there is nothing else you can do.
Check out my video on the pros and cons of Blocking.