I found the following site from The Linus Pauling Institute at Oregon State University to be very comprehensive and enlightening as to the many functions/uses of B2-from its use in the Folate cycle, to its assist in activating B6 and glutathione. It's a very busy little B!
Just have a look. I don't know that the other Bs have to divide their efforts in so many directions...
http://lpi.oregonstate.edu/mic/vitamins/riboflavin#function
http://lpi.oregonstate.edu/mic/vitamins/riboflavin#function