Launching a site does not mean your site has to be finished. I write this to introduce the concept that your site can be done in phases for budgetary, business development or content availability reasons.
There IS a point when the site can be and, perhaps, should be launched. At that point, your domain name would be redirected to the new server where your new site is hosted.
I talk to my clients at the beginning of the project and help them decide what are the most important parts of the site that need to be public first.
With a CMS, you can create sections, add to sections, etc. much easier than when you aren’t using one. This is very important if you expect to expand your site over time by planning to do it in phases or because that is the nature of your business.
One good thing about doing your site in phases is it allows you to test the marketing waters with your current content and could tell you in which direction the site needs to go in a few months from launching.
New businesses or businesses with new websites would especially benefit from this strategy. The site is one important piece of your overall marketing plan which should be revisited periodically.