If the bees wrote a book on the subject, that's what I would follow. Until that happy event, the best writing on the subject is the Complete Idiot's Guide to Beekeeping by Dean Stiglitz. Michael Bush has also offered good advice on his website. From what I've seen I would summarize the situation as follows:
1. Don't spread the broodnest out too much because the nurse bees won't be able to cover it.
2. But if the broodnest is crowded, it should be gradually opened and expanded. You can do that by putting a couple of foundationless or small cell foundation, or small cell plastic frames (PF100) interspersed among existing brood frames. No more than every third frame should be empty at one time. (So every undrawn frame would be surrounded by two full frames on each side). This should only be maintained if the bees quickly jump on the new frames and start drawing and laying.
3. As you add frames in the middle of the broodnest, move the displaced frames gradually outward and eventually up to the center of the next box. You can then continue the expanison of broodnest in two or more boxes. Don't use a queen excluder and let the queen go where she wants to.
4. This process will result in a bell-shaped broodnest with honey toward the sides, which is the natural form in the wild. As the population of the hive rises and falls and as honey stores increase and decrease, the top of the bell curve will move up and down, sometimes dropping down into a lower box. Iddee has described this as an inverted beachball going up and down with the rise and fall of water.
The above is just my assimilation of what I've read and observed. I'm now trying to adjust these ideas for a horizontal hive. I would appreciate hearing what people think happens with unlimited broodnest in a long horizontal deep.