The shovel-hook is actually a combination of two punches; the hook and the upper-cut. Why would you throw a shovel-hook? One, to mix up your punches, to show your opponent something different, to keep him guessing. And two, it lands differently on the body, therefore, it hits different areas than would the upper-cut or hook alone. It is best if you throw this punch to your opponent's body.
To throw this punch properly, drop your punching hand a few inches, then throw the punch at a 45 degree angle toward your opponent's ribs. In other words, instead of throwing it straight up like an upper-cut or horizontally like a hook, you're throwing it somewhere in between. Again, put your shoulder and hip into the punch for added power.