Why do they tell you to do this?

Ladies, I'm a slow, new-to-machinequilting quilter and have been lurking for
some time now. It's given me a lot of respect for your collective wisdom.
Please can you help ?

My problem; I've found a wall-hanging in the Kathleen Guerrier Little Book
of Little Quilts which I'd like to make, ( the Plain Sailing one). It's
foundation pieced with beach huts and sailing boats.

The instructions tell you to trace the outline of the beach huts and sailing
boats onto calico and then " turn the foundation fabric over to the side you
have not drawn on and place the first piece of fabric right side up over the
position of the centre square. Hold the calico up to the light to ensure the
placement is correct."

I'm sure I'm missing something here but why turn the foundation fabric over
? The pattern is symmetrical, I can't see how the pencil lines where you
trace the template will be seen when the block is finished and it seems to
make the whole thing unnecessarily complicated. I've got masses of fairly
thick unbleached cotton that I'd like to use for foundation but I can't
really see through it that well.

My family can't see it either !

Thanks,

Sue from Oxford, England