This is a simple modification that adds up to two by-products to the intermediate products: scrap metal with a probability of 10% for one or 5% for two scrap metal types. This scrap metal can be collected and later processed in a recycler and then smelted into plates again. It's very simple, but it adds a small layer of complexity to your transport-belt layout. In the early game you can easily solve this with splitters or filter-inserters. Later in high-production areas, you have a dedicated transport-belt.
Mods introducing new content into the game.