What can Dual-Extruder 3D printer do for you?

Nowadays, there are 2 extruder or 3 extruder 3D printer in the world. The first idea came in mind is " printer many color" or " printer fast". However, it is not totally true!! Exactly, it can print 2 colors, thus we can print this globe model. 





But it is wrong, if you think it can print faster, please see below pictures. 

Mastech globe
Mastech 3D printer, beaver iiii
beaver iii dual-extruder picture

When you are using Dual-extruder 3D printer, except main product. It also prints 2 walls, please see red arrow, there are green and blue walls. There are two meanings for these 2 walls, First, when right nozzle finish its part, right-extruder need to go to right side to get down temperature to stop filament go out, and the left-extruder is heating to make it possible to start printing. Second, After right-extruder down temperature, there is some scrap on the right-extruder, so this wall can isolate the scrap out of printing range. see the red circle of the picture. 

Therefore, because these 2 walls, the printing time will be longer.............

Thus, the extruder advantage are 1. can print two colors 2. can printer different materials. 

Like this globe, Blue is PLA filament, Green is ABS filament.