The smaller nozzles have a small nozzle tip which offers incredible precision. The larger nozzles afford you the ability to print with larger layers. 

You can easily identify all the nozzles in the series by looking at the markings on the flats of the hex head. See below to help you identify what each set of markings ( dots on the nozzle head ) means in relevance to size. 

Nozzle diameter is marked on every nozzle with drilled dots.

To get finer detail on 0.1 mm or 0.05 mm print settings, you can use 0.25 mm nozzle. But use it for only very small objects, only couple centimeters big. The print time can be considerably longer compared to default 0.4 mm or 0.8 mm