Reply To: Any real reason not to build PDF's as single page spreads?

There's all sorts of reasons to let InDesign know whether a given page is recto or verso. Not just page numbers but running heads in general, especially where you want different running heads on the left and right hand pages; you might want different margins on rectos and versos, or even have a highly visual design with, say, a line down the foredge side or a background colour on verso pages only; you might have chapters starting on rectos only, which you'd want to set with a paragraph style; you might want to align text or anchored objects to the spine or foredge, or have a paragraph rule that sticks into the foredge margin…

I suppose if you're working with a very simple design that has absolutely no difference at all between recto and verso pages then yes, go ahead and create it as single pages. But for most of the work I do, I couldn't manage without working in spreads.