Dumb question:

I am finishing up a built-in book shelf for our bedroom that I made from plywood with a hardwood face frame.  Is there any reason to apply finish to the back and side of the unit that will connect with the walls of the bedroom?  Our house is small and its winter time and I am reluctant to “stink” up the house by applying multiple layers of finish (Waterlox Original).  I was thinking that I could go ahead and mount the unit now and finish it in the springtime when its warmer and I can leave the windows open.

I’m guessing that the plywood won’t move with changes in humidity and therefore no purpose would be served by finishing the back and side that no one will see.

Thanks in advance