One of the important feature which is missing in VSTS Team Build is Continuous Integration support. Though there are lots of workaround to achieve this, there is no readymade solutions to implement this. But with TFS Integrator, you can implement continuous integration with few configuration settings. For more details, check out this blog
http://notgartner.wordpress.com/2006/09/18/getting-started-with-tfs-integrator/