At a recent meeting for Metro Parks, the Director of the Zoo mentioned something about the zoo's "charismatic mega-vertebrates." As in walruses and polar bears and tigers.
Charismatic mega-vertebrates, if you are a zookeeper, is a very useful classification. It describes a certain kind of animal that crosses biological distinctions of taxonomy: ie, big animals people want to see.
But outside of that particular setting, the jargon makes absolutely no sense. I wouldn't tell you in normal conversation that you should get to the zoo to see the baby charismatic mega-vertebrates. They're baby tigers. Calling them anything else would be dumb.
This is a kinda of silly example, but it applies equally to other worlds as well.
Take one of my other hats: web developer for Mary Holste Design.
I can be proud that I used Javascript and jquery to assemble an AJAX solution for a client. But no one else cares. Those who don't know what I'm talking about won't understand why I'm proud, and those that do understand will likely think, "Big whoop, I've done that."
But if I tell someone I'm proud because I figured out something that had been really challenging for me, and it made my client really happy, then that's something everyone can relate to. Using jargon doesn't make me sound smarter, it makes the listen feel stupider, and it takes away from the point I was trying to make.
Or in the non-profit world: donors can be classed as lybunts and sybunts (donors who gave Last Year BU N This or Some Year BU Not This). It's perfectly acceptable to talk about this within development circles. But outside that small circle, in conversation with friends, clients, or just basic socializing, there's no reason for it.
Put it in English. Your listener will thank you for it.