A thousand years of being separated has done more physiological damage than what is portrayed by the two sisters who rule Equestria. We've seen Luna apologize for the tyranny she brought upon the ponies of the land, but what about Celestia? How does she feel about it? Does she not have any regrets about what she had done to her younger sister? Having the power to view and intervene in one's dream could be useful in finding out the truth.