The setup for ADFS 2.0 installs a new service
adfssrv in addition to the ADFS website.
What is the purpose of this service? The documentation does not contain any information about it.
This is the adfs service. This service publishes the endpoints that one communicates with. So when you request federation metadata, the service responds. See ADFS console's service/endpoints for a list of URLs that are handled by this service.
The website is merely used to serve the web pages for /adfs/ls virtual directory for purposes like home realm discovery.
This is a key difference from the old ADFS 1.0 included in-box with the OS. That runs as a web application in IIS. The new version 2.0 is a separate service.