Materials allow me to quickly, easy, accurately + reliably construct my models as they would be built in real life using the actual materials/products involved. Previously all I had to work with were Components (of Walls, Slabs, Roofs, etc) but these only had the potential to contain a very limited amount of information (a Name, R-value + thickness + nothing else) + they weren't transferable across styles or tools so it was a real pain maintaining consistency. Plus there was no link between them