This is a novel idea for sure. Not sure if it will really catch on though. a Company called FaBrickator combines Legos and 3D printing to speed up the making process. Basically the software they have will substitute out lego blocks for 3D printed sections of a model. For the areas which can not be constructed with lego's it will print out with the 3D Printer you have. Doing this saves a ton of print time, often several hours. Here is an example of a 3D printed object and a FaBrickated object:



As you see in this example the faBrickated object was created in just over 2 hours time, while the 3D printed one took 6:30. The difference is that the 3D printed object is actually all one solid piece.

Here's another pretty cool faBrickation:


And now the video explaining it all: