Barbarian: Musclebound vs Smash

I don't understand the point of the barbarian advanced move called Smash when he has Musclebound as starting move. Can someone explain it to me?

From rulebook:
Starting Move Musclebound: While you wield a weapon it gains Forceful and Messy tags.
Advanced Move Smash!: When you hack and slah on a 12+ deal your damage and choose something physical your target has (a weapon, their position, a limb): they loose it.
Weapon tag Messy: It does damage in a particular destructive way, ripping people and things apart.
Weapon tag Forceful: It can knock someone back a  pace, maybe even off their feet.

Messy and Forceful are interpreted by the GM; the object of the Smash! is named by the player.

As a GM, if someone dealt only 1-2HP of Messy/Forceful, I'd say they slashed the orc's face open, and blood sprays everywhere, and the orc falls back a pace -- but I wouldn't dismember the orc. With Smash!, it's not up to me; if the player hits 12+ and wants the orc to lose an arm, it's gone.

Messy/Forceful also won't usually take away the particularly important magic item your opponent is wearing. Smash! is ideal for getting Magneto's helmet off.

Ok, thanks for clarification.