why is promoting ahead of time (via teasers) always recommended?

There are some criteria that support the idea of early promotion:

• Your product naturally has a short shelf life, and its revenue will die quickly. Then, you need to make revenue fast and early promotion helps you doing so.
• Your product's main benefit is an experience quality and can only be verified by the buyer after purchase. Then, you may need more social proof then usual. Early promotion helps you getting social proof.
• Your product's main benefit is basically due to positive network effects. You need to overcome the bootstrapping problem and early promotion helps you doing that.

For example, a new movie has a natural shelf life. After its launch, many other new movies will be released and may affect the movie's revenue. Also, it's entertainment factor is impossible to judge before purchase. It's an experience quality and thus needs more social proof then usual.

For movies, it's thus rational to spend large amounts of money on early promotion.

However, for software startups, early promotion is usually inexpensive, due to means such as blogging, social media, etc. Thus, early promotion is usually a good thing. The amount of "finish" of your product is also not a problem. People got used to beta labels.

Another nice side effect happens when you combine early promotion with (artifical) scarcity; for example, by using invitation codes. People crave scarce products that everybody (in their social circle) talks about.

This allows you to control the amount of beta testers, increases your chances of getting feedback, and prevents making truely expensive mistakes such as developing features nobody wants.

Overall, early promotion increases your chances of success.

Hope that helps.

Getting anyone to notice you exist is the SINGLE biggest challenge for any startup. I received what I think was a really good piece of advice - set up a blog early. It may take a year of quality content for you to crawl your way up the Google rankings. This is important because "natural" search traffic is far better than paid traffic (and free) and you can start building a base of eager early users.

I'd recommend you check out Eric Ries' http://www.startuplessonslearned.com/ It isn't some much "marketing" but customer development. (note that this blog is not displaying in IE right now). Eric would suggest you start testing whether your market is viable right away (search the blog for "smoke test")

Teasers and such can create buzz. We want to feel "in the know" by being part of that buzz and share it with others to feel empowered ourselves and feel like we're giving value to others. Buzz creates curiosity. And most of us want to know what's not completely in the open if we might derive some value from whatever product or service it is. When Google was handing out select invites to Gmail it was insanely hot. Could have been a horrible product but we wanted it because we couldn't have it easily.

The one big thing you've got to be careful about is timing. Teasers and buzz creation should follow a pretty structured timeline. If your product suddenly slips out from launch way beyond expectations then you can potentially do more damage than good.

You also have to be careful from a competitive standpoint. At Borland many years ago we were preparing to ship Quattro Pro (name from the past) as our Windows spreadsheet. We started giving previews, showing at tradeshows and more. Unfortunately development pushed out way, way beyond expectations. Microsoft videotaped presentations and butchered the features into Excel. By the time we shipped it looked like we were copying Microsoft. So take all the factors into account.

Best of luck.

two words - Mind Share

try to read up on Seth Godin's Purple Cow also :)

There are certainly times when you should not promote ahead of time. For example, if you're releasing a V2 product with many whizzy features and you promote it early then people could stop buying V1 and wait for the upgrade. This is what killed Osborne Computers.