Spending money on web design without defining a search engine strategy is like building a store underground—you will miss important traffic and thus potential revenue. Trying to fix it later on costs both time and money.
Working with a Drupal shop that understands search engine optimization allows optimisation to be incorporated early on in the design process.
Search Engines usually find your site by following links from other sites or when you submit a site map to an engine. They then find the deeper pages in your site by following internal links within your site. If your navigational structure is poorly planned, the search engine will not find all of your content.