Not exactly. I'm saying that in yEd, you decide about the real world size of your diagram not before exporting. Since most export commands support fitting the diagram into any given dimensions, your diagram can always match the desired page size, and since the internal representation of the diagram is vectorized, this scaling comes without loss of quality.
Of course, if you choose this option and the diagram is very large (in yEd coordinates) then elements might be pretty small in the exported file and you have to increase font size etc. to maintain readability. Nevertheless, with yEd's frictionless zooming and moving of the drawing area, the elements under consideration can always have a nice size on the screen.
