Air = air in weight so open areas of construction are ideal and I'd be hesitant to fill them with something that is heavier than air when a need does not exist. In the past 40 years we've moved away from solid sheeting and I see that as a good thing. The covering material serves as the skin and strengthener and provides resistance to twist and torsional flex of many open surface areas and does so without the weight of an underlying balsa surface.

That the under surface might seem vulnerable when lifting the plane is a good trade for the weight savings of not sheeting over the stringers.

One good example of construction differences is the Ultra Stick 120 by Hanger 9. The second iteration (Ultra Stick Lite 120) was the exact same planform as the first but 2.5 lbs lighter than the first. That is 20% weight savings with a resulting much better flying plane needing a less powerful engine, the first needing a 1.6 engine and the second very happy with a 1.2.

So... I'd say, don't go sheeting happy. Second, aircraft ply should be restricted to firewall and gear support. Third, lite ply should be lightened with generous holes wherever possible. Fourth... trust the covering to add the final degree of strength needed for integrity.