Digital BW, The Print

In Amadou Diallo's book, and other places, I have read that if you use 
an empty adjustment layer with a blending mode change, the file size 
will not grow.  When I try to do this, my file size grows like with any 
other adjustment layer.  I open a new adjustment layer (usually curve) 
and OK it without any changes made.   At this point, the file size has 
grown.  What am I doing wrong?

Thanks,
Peter