The nozzle size of 0.5mm is fairly common as is 0.4mm. Smaller nozzles give you the opportunity to use smaller layer heights and finer detail at the expense of longer print times. The smaller nozzles are more sensitive to tuning changes and can clog more easily with cheap quality filament.
I printed some miniature models for my son that would not print with a 0.5mm nozzle. I bought a 0.2mm nozzle and a 0.35mm nozzle (which was half way between 0.5 and 0.2) and was able to print the models he wanted (six of them in different colors, 20+ hours each). I have since used the 0.35mm nozzle more than the 0.2mm nozzle. I routinely do .25 layer height with the .5 nozzle, .14-.18 with the .35 nozzle, and .1 with the .2 nozzle.
Changing nozzles can be a delicate process prone to error if you aren’t careful. I bought separate tool heads so I only had to do the swap once.
If you want to print some of the exotic filaments, you may want nozzles made from something other than brass. For the TAZ 6 and Mini that have auto bed leveling, you cannot use the ruby tipped nozzles as ruby doesn’t conduct electricity which is needed for the leveling process.