Having a well-stocked toolbox gives me joy, because I like having the right tool available whenever I need one. There's no need to go through and evaluate every single item in there; the toolbox takes up the same amount of space whether it's full or nearly empty.

I would have said "utility" if I were writing it, but if "joy" reaches a greater number of readers, then it's probably the better choice. And you knew what she meant, anyway.