It really depends on a company, a budget and a workflow. I worked as 3D artist where our team had to make really simple proxy meshes, just for level prototyping, collision testing etc. However, we bought several packages of props, which we used to test lighting, level design etc. Most of them were replaced by unique models done by freelancers. Marketplace allows you to quickly test and iterate your ideas, and sometimes those assets are good enough for a final game. As for myself, I only buy packs that can be used in various projects and it’s hard to tell if they had been created just for particular project/game.