Before I even read the replies I'm going... Let's not! Let's don't even bother to talk about it because no one is ever going to agree on it and there no real consensus since brand new blade manufacturers will sell you a brand new blade in different types of sharpness, coated/dipped and paint, or not extremely sharp to begin with.
If there was one right or wrong way you would assume that by now the manufacturers would have all gotten on the same page and that's how they would come when you buy a replacement blade but it's not the case so everything else is simply going to be personal preference and then reality it makes little difference.
So much so that I get multiple mowers in every single year with the blades on upside down and the customers had no idea!
Now, I'm a lot more repair guy and not a landscaper so I fixed them but I don't use them but even I in my total disregard or care for lawns and grass can usually spot grass that's been ripped apart or roughly jaggedly chopped as opposed to cut with a somewhat sharper blade but the fact is most people can't tell the difference.
That thin piece of metal is spinning so quickly that whether you want to argue about 45, 33, flat spot on the very edge, or sharp as a razor, it's going to make very little difference and anyone who thinks they can tell the difference I could set up a demonstration and I guarantee I could fool you among 20 mowers.
So as I said, I guess it's fun for conversation but let's not worry too much about it.