Actually I learned a theory from Steve Ganz about the rosette worth sharing, if not the intent of your post. But maybe there is some similarity.
The rosette may serve to prevent cracks from propagating along the grain in the soundboard where exposed at the soundhole. Likewise, the wood strips (I forget the technical term) around the outside of the top and back can prevent the beginning of a crack in a vulnerable area.
And they are a beautiful fingerprint of the luthier.
All this time I thought I was making music; it was making me.
2015 Steve Ganz "Solidarity"
1980 Dauphin D30
1962 Fender pre-CBS P-Bass
National Triolian Uke ca.1930
Almost as many fly rods as guitars