How much does site maturity impact SEO? Should I register my site before it's complete for SEO purposes?

How much does site maturity impact SEO? Should I make an “under construction” page and register my site with search engines before it’s up and running for SEO purposes?

Instead of putting up a standard “Under construction” page I would put up a page of text describing what will be on the site. This way if search engines find it they will know how to index it.