Here is the original picture I took of my sister's dog that we are watching at my house while she is on vacation. There was no light on in the room, only natural lighting from the Sun shining into the window from the left side. As you can see, it is fairly dark for this reason.

Here is the brightened version. I increased the fill light to almost half of the original and increased the highlight just a bit. The picture looks much more natural and brings a softer feel to the dog as well as the feel of the carpet.