9. Special Functionality

You may need special functionality to make your site effective.  The special functionality could be as simple as a custom inquiry form, an email form (to combat those spam-bots), the ability to search, etc.

The value of this special functionality to your site needs to be weighed against the cost. 

Each industry has special functionality that is almost required for any site.

Some companies include special functionality to set them apart from the competition.

Do you need special functionality?  There is no one answer for everyone, but looking at your competition could be a good place to start.