This is a special scenery items that allows you to display products as static scenery. This is useful for displaying products around Multiple Industry New assets or ProtoLars / Industrail type assets to provide some extra environment using meshes that match the products that will appear on the rolling stock.
The product attacher is capable of displaying any bulk or container asset. For bulk assets, it will show a pile of the material, and the amount is adjustable. The pallet is only displayed in surveyor and won't appear in game. It's basically a handle to allow you to easily move and rotate the object.
Some folks were using rolling stock, adding items to the queues, and burying the rolling stock into the ground to create a similar effect. This is more framerate and memory friendly since the rolling stock item won't be loaded.