There is power in a simple API, giving you the ability to deploy new features and functions quickly. The advantage of simple APIs is that they can be quickly and easily used.
In the case of my WordPress blog I use the Dynamic Text Replace plugin to provide quick ways of adding extra detail and information to text used often, allowing popup information or a new page with extra details to by quickly linked with a short code. The API functions within WordPress allow this integration to occur very simply by installing the plugin, detailing the code to write in the blog, and a replacement that it is exchanged with.
Other API are available, such as that used by LinkedIn to provide information on individuals in their system. This can provide information to add detail on people in your blog. As time goes by, API will be expanded and extended and offered by many more data sources (possibly for a price). These will add to the richness of the Internet.