Ask HN: What are the pros and cons of "building buzz" before launch?

We're about to launch a new product.

The approach we're most confortable with is that of a fairly soft launch: announce the product via Twitter when it's live and ready to rock and take it from there.

But after spending time with a lot of people I respect here in San Francisco, I'm starting to question that. Most people I speak with advice me to build buzz, hype, drop hints about the product, launch a teaser / holding page, etc.

Would love to know your thoughts on this please.