What's the difference between a fixed split and a fully-separated split keyboard?

Fixed-split boards (like the Logitech Ergo K860 or Perixx PERIBOARD-512) angle the left and right halves on a single chassis, which is easier to adopt. Fully-separated splits (like the Kinesis Freestyle2 or Advantage360) let you place each half independently, which shoulder-width users and trackpad-in-the-middle setups benefit from most.