Originally Posted by landshark
It is a matter of reason. A notch lapel is the most informal variation. For a formal jacket, a more formal lapel is called for (i.e. a peak or shawl lapel).
Actually, not at all. The reason, if that, is simply because cheap makers started using their normal suit patterns to make tuxedos, just adding the satin and covered buttons. So while notch was always a correct option, and chosen by accomplished dressers at the same rate as peak or notch, it was soon avoided by those who actually knew what they were doing to distance themselves from the masses in cheap and badly cut jackets.
There's no actual justification beyond that. Yes, people have tried to stretch and invent a reason afterwards, but those should be ignored. It's snobbery, but good snobbery. Somebody has to take a stand against black suits, made with shiny lapels, worn with long ties and bad wing collars.