Protect the device from what? The device needs a fault to draw more current to blow the fuse. If you have a power transistor go and you blow an internal fuse, yes it will protect the power supply from becoming the next bit to let the magic smoke out, but the transistor is already destroyed.
If you try driving some silly impedance speakers you might blow a power supply rail fuse before the transistor cooks, but that is the only situation I can think where a fuse can protect a device from damage. Most cases they are there to reduce the extent of damage once something has failed.
If you try driving some silly impedance speakers you might blow a power supply rail fuse before the transistor cooks, but that is the only situation I can think where a fuse can protect a device from damage. Most cases they are there to reduce the extent of damage once something has failed.