I can't seem to find any explanation of what lenses are used for in practical examples. This short paragraph from the Hackage page is the closest I've found:

This modules provides a convienient way to access and update the elements of a structure. It is very similar to Data.Accessors, but a bit more generic and has fewer dependencies. I particularly like how cleanly it handles nested structures in state monads.

So, what are they used for? What benefits and disadvantages do they have over other methods? Why are they needed?

haskell data-structures types lenses
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