What are fuses used for?


I have, I’m sure to many, a very dumb question. I keep reading about fuses.  I have a fairly sophisticated system and have never come across the need for a fuse.
Can someone tell me where these fuses go and what they’re used for?
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They are used to prevent damage to electric circuits from excess current. A fuse is a fine piece of wire with a selected melting point placed in series with one leg of the incoming AC voltage/current. If an electronic device draws too much current the fuse wire will melt and open. Preventing any AC voltage/current from entering the device. Thereby saving the device/circuit from further damage.
All electronic devices/circuits require fuses at the inputs to the power supplies. The exception being battery (DC) powered devices where maximum current draw is limited by the battery size.
Contrary to popular misconception by the ill-informed fuses (like all wire) have NO effect upon sound quality. To think otherwise is to believe in magic!