I'm not that sure what it is used for.
Unaware protects you from your opponents stat changing moves.
It protects you from your opponets moves that change your Stats. For example, if your opponet uses growl, it will do nothing, but if it uses swagger, you will not get better attack power. (correct me if I'm wrong)
Hope this helps:)
I think it makes the pokemon unaware to ability changes. For Example a Gardevoir has the ability "trace". It copies the foes ability "unaware". This has no effect because of the ability, basically, no pokemons ability can change while the "unaware" pokemon is out.