I have seen a couple pictures where people have put foam between the fusealage and the wing. Is this recommended? Any drawbacks? Advantages? I have noticed that on my Hobbico Avistar I get a little bit of scuffing from the fusealage on the wing.

The foam is called saddle tape and is available from most hobby stores. It does provide some cushion for the wing and also helps seal the fuselage from exhaust oils and dirt. I know of no drawbacks, it's cheap, easy, and recommended.

The foam also tends to provide a good tight fit which is important for wings with dowels on the leading edge. If a wing sits on the mount loose it will wear the mounting holes the dowels insert into.