Deploying to IIS means that Web API applications have two settings for custom errors. One for the ASP.NET WebForms/MVC applications (web.config) and one for Web API. Having the ability to link the two would allow for one config-based setting to be used. See:
http://lostechies.com/jimmybogard/2012/04/18/custom-errors-and-error-detail-policy-in-asp-net-web-api/
And
https://github.com/WebApiContrib/WebAPIContrib/commit/27381146d65b3958cf267e7bb7fcd80e1b913b66
http://lostechies.com/jimmybogard/2012/04/18/custom-errors-and-error-detail-policy-in-asp-net-web-api/
And
https://github.com/WebApiContrib/WebAPIContrib/commit/27381146d65b3958cf267e7bb7fcd80e1b913b66