Fibers, what for?

[Patric Dexheimer via Digitalmars-d-learn]

I learned about Fibers on D, and now i´m starting to read about 
it (Threads/Fibers/Coroutines) etc.
But when i try to make something usefull with it i just fail to 
see the real advantage over a normal structured programming 
without it.

Can someone show some code with usefull/unique/advantageous use 
of fibers?
Thanks in advance!