The crown cap allows you to get closer to your work and thus achieve finer detail, whilst still protecting the needle. It also decreases paint build-up on the needle and in the nozzle cap, preventing spitting.
Both of these benefits are obtained due to the better air displacement provided by the cut away sections of the crown cap. The cut-outs allow air to displace when you are getting very close to the work surface, so a crown cap is a great accessory for doing fine detail safely.
