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?
128x128Ag insider logo xs@2xrvpiano
It is also possible if you have newer gear there maybe NO "user" accessible fuse to change.
There has been a trend to just solder a fuse internally on a board.

Obviously not something you can just switch out quickly and easily.

Some even more enlightened manufacturers have abandoned fuses altogether in favour of circuit breakers.
I think I’m going to be a flatearther on this one.
It seems like too much trouble.
Post removed 
OP
Probably a very wise decision... Lol.
One more item not to fret over or spend money on!