Voids can be a very useful object in complex form modelling. If you need to create a complex structural form you can use the edges of the void as a path to help host sweeps. As the void is negative space it won’t be visible in the final model.
It is a lot easier to create paths on the edges of a void form rather than having to try and create the path as a line. This is evident when you have to distort the path in 3 directions, (It is possible to do it using an adaptive family with points and splines, but is just so much simpler to use a void).
In the example I am using an extruded blend to create my void form.
Once you have the edges looking correct, just host a sweep to the edges using the ‘Pick Path’ and your complex form is finished.