Depends on what you are launching. A weekend project? Just get your work in front of people. Something you spent six months in stealth mode working on? Sure, get it all set up before launch during the development process.

Can't say I agree with you. Even with weekend projects I'll throw some analytics and other quantification tools in from the beginning as I want to see what kind of traction it gets. How else would I even begin to know if there's interest in what I've created?