Running applications also have labels. For example, your web browser may be running as firefox_t. Type enforcement simply allows you to specify what application label can access what resource label. In the most simple terms SELinux lets you allow an application to do something with a resource:
A (deserved, but outdated) reputation for breaking things and being hard to configure, nonexistent or inferior toolsets on non-RPM distros due to lack of support on same.
http://selinuxproject.org/page/FAQ#How_does_SELinux_work.3F