So I put balsarite on my wing getting ready to put on monokote. So do you a lite sanding to get it smooth before the monokote goes on?

My guess is yes.

Thanks
Paul

In my experience with balsa rite I have never sanded it after application to the surfaces to be covered.  When you iron the covering down it will smooth out.  Using it in engine compartments, I usually put a second coat on without sanding.  MERRY CHRISTMAS,  DOC Holliday

I've been using monokote since it first came out as a wet glue covering and never had to use anything to get it to stick.
Perry Rose

Balsarite for film isn't a glue (unlike the original Balsarite that you use for fabric coverings), but more like a balsa conditioner. It hardens up the balsa surface (but not as hard--or heavy) like epoxy. It is also a fuel proofer, so maybe is a good choice around a fuse or anything that you intend to cover with plastic covering material.
Any the hardened balsa surface does provide a nicer grip for the plastic covering adhesive, but as Charlie Bauer use to tell us in his monocote covering demo---he never used anything other than monocote. He did say tho' that you want a nice smooth dust-free surface.