Who came up with the idea of diamond-plating steel or other sheet metal and why? Other than decoration, it doesn’t seem to serve any purpose; I hardly ever see it except on toolboxes and running-boards, and although it looks really cool, it obviously costs more money than just a flat piece of stainless steel. What gives?
It provides better traction for stepping/walking on. Like you said, it looks pretty good too, which for a lot of people is reason enough,
It provides better traction than a smooth steel surface, especially if you have work boots on. IIRC the patterning also makes it slightly stronger by distributing internal stresses, and making it more rigid.
I always thought it was to improve traction by giving the surface of the steel some texture. This would be especially important on a wet running board, even if you’re just using it to step up into a vehicle.
In my experience, that diamond plate metal is usually aluminum. It comes from more industrial settings such as power plants in the like.
In all of the engine rooms where I served my Navy time, the deck plating was made of diamond-plate aluminum. It was very convenient to access the bilges (just pop up a few screws in the corners and lift the panel), and the diamonds gave a degree of traction that a plain sheet of aluminum would not offer.