Most large furniture in a modern home was built in place. It was carried in flat-packed, assembled in the bedroom, and has never needed to come back out whole. Moving house is when that becomes a problem.
A king-size bed frame won't clear most internal doorways. A double wardrobe on a Victorian staircase can't come down in one piece. Large corner desks, tall bookshelves and big dining tables all cause the same issue in tight terraces, narrow flats or houses with awkward stair layouts.
Flag the items when you book. The driver works through the disassembly before loading, keeps all the fittings and hardware together during transport, and rebuilds at the destination. A bed each way adds roughly 30 to 45 minutes. A wardrobe adds more. Two or three pieces at each end can add a couple of hours to the job total. None of that changes the hourly rate. You're just booking more time.