When a group of people talk to each other a lot they develop terms that they can use in place of larger concepts. This makes it easier to talk to people inside the group, but then it's harder to talk about the same ideas with people outside the group. If we were smart enough to keep up fully independent vocabularies where we would always use the right words for the people we were talking to, this wouldn't be an issue. But instead we get in the habit of saying weird words, and then when we want to talk to people who don't know those words we either struggle to find words they know or waste a lot of time introducing words. Especially when the group jargon term offers only a minor advantage over the non-jargon phrasing I think this is a bad tradeoff if you also want to speak to people outside the group.
Recently I've been working on using as little jargon as possible. Pushing myself to speak conventionally, even when among people who would understand weird terms a little faster, can be frustrating, but I think I'm also getting better at it.
I also posted this on my blog
Unless the jargon perpetuates a false dichotomy, or otherwise obscures relevant content. In politics, those who think in terms of a black-and-white distinction between liberal and conservative may have a hard time understanding positions that fall in the middle (or defy the spectrum altogether). Or, on LessWrong, people often employ social-status-based explanations. We all have the jargon for that, so it's easy to think about and communicate, but focusing on status-motivations obscures people's other motivations.
(I was going to explain this in terms of dimensionality reduction, but then I thought better of using potentially-obscure machine learning jargon. =) )