A significant benefit that custom keyboard firmware allows is reduced finger movement. Though mostly this is more sophisticated than just changing between qwert

A significant benefit that custom keyboard firmware allows is reduced finger movement. Though mostly this is more sophisticated than just changing between qwerty/dvorak. e.g. pressing a shortcut like "Ctrl + b" most likely involves stretching your pinky finger on a standard keyboard. One feature custom keyboards often have is dual-use keys; keys which act the same if tapped, but have a different function if held. So e.g. tapping 'f' outputs 'f', holding 'f' is the same as holding 'shift'. With that technique, you can put Shift, Ctrl, GUI, Alt all on the home row. Custom firmware can also support chords; e.g. pressing 'cv' at the same time could be a chord to switch to the previous virtual desktop. Custom firmware also allows layers (similar to how some laptops have a 'numpad' in the middle of the keyboard which can be used if Fn is held). This allows more flexibility, at the cost of more complexity. Much of this could be done with e.g. kmonad, but it's nice to have it on the keyboard itself.