The 4″ offset is typically used to bridge over a lower protruding brick water table.
The 4" offset is typically used to bridge over a lower protruding brick water table, or other constructions that requires you to move slightly from the center of your downspout. The 4" offset have an expanded top and shrunk bottom end to fit outside and inside the downspout. For reference the 70° elbows connected together gives you an 7.5" offset. There is no need for caulking or putting any rivets or screws into the system. In most other systems caulking and putting screws in the flow of water results in debris being clogged, increasing the risk for leaks.
White, Black, Anthracite Metallic, Silver Metallic, Dark Bronze