Not necessarily, any model that is manifold, that is, fully "enclosed" without its interior or backfaces exposed, can be made hollow, which is the main saver of print material, whether resin or filament.

I've also found some models, back before the pandemic, that had loose vertices, unconnected to anything. When slicing, they'd create several faces that were only visible in the sliced file, fucking the print. Always good to get at least a basic understanding of blender and 3D models before printing.