Bypass

This transformation simply passes its input image through to its output image. It has no settings or dialog box.

Bypass can be convenient in connection with other transformations such as Composite, Filter, etc. that accept auxiliary inputs. In the example below, Composite is operating on the checkerboard image using the full moon image as an overlay. If you want to insert a transformation after the full moon image, for example to lighten it, Composite will still be operating on the original full moon image since it is the image selected as the Overlay.

If you insert a Bypass after the full moon image and use the bypass output as the input to Composite, then you can insert new transformations between the full moon image and the bypass image and the changes will flow through into Composite.

If you prefer not to use Bypass, you can always edit the Composite transformation to change the Overlay image and Overlay Amount instead.