An ordered list of filters would limit the user to providing one input image and producing one output. Using a schematic editor allows for combining multiple in

An ordered list of filters would limit the user to providing one input image and producing one output. Using a schematic editor allows for combining multiple inputs and perhaps even producing multiple outputs from one schematic (the gif on the home page doesn't show this so I don't know if they support this). Of course you don't need a schematic editor for that, you could also use an expression language with variables. But for people not used to programming that tends to be a bit intimidating.