With the announcement of MakerBot's giant Replicator 3D printer, we're now entering a stage where most personal 3D printers have a significantly large build envelope, typically around 200mm wide by 200mm deep by 150+mm tall. This means we can print big things! But should we?
Sure you can print something "twice as large", but what does that mean? Usually it means printing the a 120mm cube instead of a 60mm cube. In other words, when we say "twice as big", it usually means one of the axes has double length.
This leads to a big issue that owners of large-sized personal 3D printers must face: print time. When you "double the size" of something you must consider that the actual object volume goes up twice x twice x twice = eight times the volume. This often means a print time of up to eight times as long! So your 47 minute print suddenly becomes six hours and sixteen minutes!
But wait, it gets a lot worse. Everyone prefers higher resolution prints because they're visually more appealing with their smoother finish. The same equation results when you double the resolution: if you're printing at 0.5mm resolution and change it to 0.25mm resolution you've just created (more or less) eight times as much work to do! So even at the same physical size, a higher resolution print can take much longer.
The situation is worst when you double the size of an object and also double the resolution: a theoretical 64 times longer to print. Of course these numbers are simply theoretical as the actual print time depends on a variety of factors, not the least of which is the number of shells, the complexity of the geometry and the fill density and pattern. Maybe it means we'll all be printing things overnight instead of while you wait.
Nevertheless, the moral of the story is to carefully consider your print time when you get your brand new giant 3D printer.