Advantages to heated bed:
•Easier to get PLA to stick.
•Pretty much required for printing ABS.
•Reduces warping all around.
Disadvantages to heated bed-
•Scarcity, especially for huge printers. The only heated bed of that size that I could find was http://store.quintessentialuniversalbuildingdevice.com/product.php?id_product=113 . One workaround is to tile a few smaller heated beds and heat up "zones" of it.
• Proce. Price increases a lot as the size increases. For example, the heated bed I linked is over $250. Again, tiling can be a solution.
•Electronics- not very many electronics can handle heating such a large area. Make sure your PSU (and house wiring) can handle almost a kilowatt load on one outlet. If you choose to tile, note that not very many boards/firmware will support it well. (Note that if you can control the heat individually for each tile, you can save power by only heating what you need to).
Note that with any heated bed, temperatures tend to drop off toward the edges. Make sure your heating is even if you tile.