When building a node group that's meant to be used directly in the
node editor as well as in the modifier, it's useful to be able to have
some inputs that are only meant for the node editor, like inputs that
only make sense when combined with other nodes.
In the future we might have the ability to only display certain assets
in the modifier and the node editor, but until then this simple solution
allows a bit more customization.
Hans Goudey