Normally it will just use only one - in most cases the Ethernet as it should be faster
but there is some programs that can use both at the same time ---} Combining Both Speeds
i believe (Dispatch) is one of them - it is from the company that made (Connectify)
the problem it's quite expensive - but you might need it if you want better speeds
---Update
now it's called Speedify
here is the link for Website
http://speedify.com/