I've read that Lua is often used for embedded scripting and in particular game for scripting. I find it hard to picture how it is used exactly. Can you describe why and for which features and for which audience it is used?

This questions isn't specifically addressing Lua, but rather any embedded scripting that serves a purpose similar to Lua scripting.

Is it used for end-users to make custom adjustments? Is it used for game developers to speed up creation of game logic (levels, AI, ...)? Is it used to script game framework code since scripting can be faster?

Basically I'm wondering how deep between plain configuration and framework logic such scripting usage goes. And how much scripting is done. A few configuration lines or a considerable amount?