When I read the labels on canned tomato sauce, there are always "flavoings" meaning herbs and spices, and there is also green peppers. Tomato puree is simply tomato, sometimes tomato juice, and salt.
I like using crushed tomatoes, or tomato puree as my starting point, as it's as close to fresh tomatoes as I can get, without canning my own. It's a blank slate, so to speak, that allows me to flavor my sauce however I desire, and for whatever purpose I'm making the sauce for. In other words, it's more versatile than is tomato sauce.
Turning puree into sauce can be as simple as adding a little onion and garlic powder, or as complex as making a Bolognase, or a Tomato Sauce (as in the French Mother Sauce).
Seeeeeeya; Chief Longwind of the North