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?
128x128rvpiano
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Interesting how the majority of those who have upgraded to the SR Blue fuses hear a pronounced improvement in their systems, and how few hear nothing or just a slight improvement. What explains this? 

Frank
It’s explained by the fact that people spending 150 bucks on a fuse really NEED to hear an improvement or they feel like they’ve been duped, and also feel the need to join a support group (like the ones here) for the same reason. Most audiophiles and gear manufacturers (like Roger Modjeski) don’t care at all about "magic" fuses...what explains this?
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