Why it’s important
The needle cap protects the needle from the work and the work from the needle.
Removing the needle cap decreases the spray pattern’s spread just a bit. This allows you to spray finer details, however there is a risk once you remove it.
If the surface is harder than the needle’s tip. i.e. Car door, block of wood, statue. You’ll bend your needle tip if you get too close. You might be able to straighten it back out and polish it up just like new, but I normally tell people to go get the new needle anyways.
If the surface is softer than the needle’s tip, i.e. skin, you’ll scrape and hurt them. For those of you playing along at home THAT’S BAD! So for you, don’t remove your needle cap!
If you’d really like to try out this extra-super-duper detail trick yet keep your needle (or your client) protected you might look into some of the solutions airbrush manufacturers came up with.
Iwata calls theirs a crown cap.
Care and Feeding
Cleaned out a clogged needle cap with a cotton swab dipped in the appropriate cleaning solution. Do make sure you get all the cotton fibers picked off if any decide to stay for a long relationship.
Damaged or bent caps tend to build up paint quicker as long as the threads haven’t been damaged.