Let's say that you have a DirectAccess connection to the corporate network. DA works automatically, so you don't need to turn it on, which is quite cool. However, DA requires that the client be IPv6 aware (the server side doesn't need to be, but the client must be).
What if you have a client that isn't IPv6 aware?
In that case you can establish a VPN connection to the corporate network. But what happens to the DA connection while you're connected to the VPN?
It depends. In most cases the DA connection will turn itself off, since it will be able to resolve the name of the Network Location Server (NLS) and connect to it over HTTPS. When you disconnect from the VPN server, this will cause a change in network state, which will trigger a DA detection again for the NLS. When the NLS can't be contacted, it will cause the DA components to turn on again and you'll be connected over DirectAccess.