If you have a WordPress site, you will know all about the great range of themes available for you to use. There are literally thousands of free web themes for WordPress users to install, allowing for almost limitless designs and functionality.
Choosing a theme is important, as the theme is what makes the site look a certain way. You should choose a theme which reflects your company as well as the purpose of the site. If for example, you are planning to sell products through your site, you will need a theme which supports ecommerce.
Other companies might prefer a theme which displays their photos and blog posts in an attractive way, others might like a theme which has multiple pages and customisation options. Customising the theme allows you to make the site completely unique for you, and different from any other people also using the same theme. This is the only danger or drawback when using built in themes – there will always be other people using the same theme!