Commanders that do this well are Roxanne, Starfall Savant, and Jolene, the Plunder Queen, doubling your treasures and increasing their effectiveness
The fact that it has built-in protection in the form of basically Hexproof
This means you could spend the mana to activate an ability of a permanent with changeling (a keyword ability that gives it all creature types) or a Hero card in your hand or graveyard, for example
Just casting your commander and following it up with a removal spell is a good tempo play, too
Eminence is an inherently powerful ability, and I've played many games where Edgar didn't even need to leave the Command Zone to win the game
Flash, Flying and a big butt can make this card a very potent surprise blocker when opponents don't expect you to cast your commander on their turn, but Nymris' real power lies in the card draw ability