What is the purpose of a flatbed trailer on semi truck?

Flatbeds are commonly used to transport unusually shaped loads, or even loads that are too large for a closed van trailer — in other words, those that wouldn't fit in a typical box truck. These include construction equipment, heavy machinery, metal beams, steel siding pipes and other industrial goods. With flatbed trailers, cargo can be secured directly to the trailer's frame, platform or the deck in a way that's flexible and customizable to the load size.