My printer (Creality CR10S Pro) came with a 0.4mm nozzle and I have never strayed from that size despite upgrading the hot end and the nozzle. It seems that pieces about 1/32" are the thinnest I can print with this nozzle and still get decent results. I'm using regular old 1.75mm Hatchbox PLA.
Has anybody achieved any finer detail with smaller nozzles? I expect FDM printers will have layer lines no matter what size nozzle is used but being able to achieve thinner details would be cool.