Questions about the gameplay of Heroes 6.

The meaning is the same; you will be playing as Anastasia, but as a different character. I wrote a little earlier about how to start playing; simply press + at the beginning of the campaign and create a new hero, and as I wrote before, all game saves in this campaign will be lost. So be careful; you can try creating your character in any other campaign that hasn't been started yet.
And yes, regarding the meaning, it seems to me that it would have been easier for the developers to make the choice of a special ability for the main hero, rather than creating an unnecessary function.