That's incorrect. If you want a flat surface via planer, you will need to join a face first. And most times bodies are edge joined by at least two pieces.....heck a lot of big name geets are three or more. Just as strong.
Sorry dude, but I'm with K on this one. I've done it many times, and it works great.
From a rough piece of lumber:
1) Plane face A until all of the rough surface is gone. I usually do it in 1/64" incriments. It will NOT be perfectly level because B is not level yet.
2) Plane face B the same way. B will now be ALMOST paralell with A.
3) Re-do A with a pass or two to make it level.
4) Re-do B.
Now you're totally level.
But that only takes care of the wide surfaces. We're dealing with 4" - 14" wide pieces that are usually 2"+ thick. That's why you need a jointer. Before I had one, I was trying desperately to true up the "thin" sides with a table saw, but it just didn't work.
Bottom line, if you're gluing pieces together to make the final width, you need a jointer.
Dude, His dudeness, duderino...I like that.
Anyway, unless you do special preparations such as Fryovanni mentions with his shimming and straight edge technique you're fooling yourself if you think that your are getting it flat by merely flipping the stock. But, hey there are more than one way to skin a cat. We'll just agree to disagree. I'll keep doing it my way.
Gil