Yes it is used for lubricating moving metal parts. I consider it
necessary. The part that wears will be the needle, so you will eventually experience degradation of quality. A bottle goes for around $5, so the next time you order something online, see if the store carries it. That bottle will last you a very long time as a little dab will do ya.
I've heard it's basically glycerin which can be bought at the local pharmacy. You don't want to use 3'n1 or sewing machine lube as that can end up in your paint job.