On my spindle moulder, there is an adjustable end-stop
You can flip it out of the way. I use this type of thing on my SCMS. You slide your wood along until it hits the stop and then make your cut. Uniform lengths result.
But on the spindle moulder that wont work because you have the fence - like this
so the wood has to be the right length to start with.
(Note to self......clean and tidy the floor before taking photos )
So what's it for?