As explained in the Printing Head dedicated page, the size of the most important component of the extruder can be replaced and changed easily. This is the perfect solution when it is time to clean everything up or to switch to a different width.
As a normal maintenance procedure, the nozzle should be always kept clean and free from debris or melted filament: this will reduce the risk of clogging and will avoid burnt material to crystallize around. The cleaner is the nozzle the better the filament will flow.
Normally, it is better to always unspool the 3d printing filament or material so that nothing stays inside the head too long. This is even more important when changing from ABS to PLA (and viceversa, as well as with others) as they have different melting points.
Referring to the size, the FABtotum is now equipped with a 0.4mm one, but a 0.6mm is as well available. The standard one is a balance between a top-quality result and a fast and easy extrusion: while the technology itself is still slow, the development is striving to find solutions to add speed.
This last point is why a 0.6mm might be preferred: having more material fed means the chance of going quicker. Layers, as a consequence, will be thicker and visible. A wider nozzle can help when printing those special filaments that contain percentages of fibers: wood PLA, glass PLA and so on.
The hot end’s nozzle is the final part but the height of the layers can still be adjusted: when setting the file before printing (see “Slicing”) it is important to always double-check everything is well tuned so that the size and the layer height is well set.