Copywriting is a very important aspect of Search Engine Optimization. In fact, it is the single most important factor that makes a search engine pick up your site. The right copy ensures that
There is relevant text on the site.
Content is specific, not generic.
Text targets traffic, makes search local (For example, 'free email UK').
Content segments your target audience (For example if you sell nutritional supplement then adults, pregnant women, growing teenagers, children, senior citizens, athletes, and many others could be your audience!. While all of these may seem to be entirely different target markets, they are actually just segments of the same nutritional supplement market.)
Your home page gives general information that is applicable to all your site visitors.Breaks out the information specific to each segment of your market.
Gives a brief description of the details of each segment and sub segment with their links. (This is important for SEO, as many key phrases come from highly specific search, instead of "nutritional supplement", you might find that "nutritional supplements for athletes" will give you the high rankings you want.)