Do check out the links in my original comment above, which explain that the whole motivation behind all this (of which lenses are just a small part) is modularity. Modularity and composability are two sides of the same coin---being able to construct a complex whole by combining simple parts---depending on whether you view it top-down or bottom-up.

Suppose you refactor a field `T.e.a.d` to `T.e.b.d`, for whatever reasons. How many places in your codebase will you have to edit, to complete this change?

Dot access exposes to the outside world the implementation details of where `d` lives, while lenses allow you to abstract that as yet another function application (of a "deep-getter" function) so your code becomes extremely modular and flexible. A good language implementation then hopefully allows you to use this abstraction/indirection without a significant performance penalty.