Topic-specific vocabulary and technical jargon has to get finessed to be used properly. In a perfect world, you can use such words in a way that the context makes their meaning clear. Or, at the very least, gives an obvious way to research what the word means. Acronyms and abbreviations are an excellent anti-example for this - I'd never use an abbreviation unless it's absolutely necessary, and use the full phrase nearby before it. Garbage-in garbage-out is a useful way to talk about algorithms failing by seeding them with bad input, but randomly dropping GIGO in a conversation is a quick way to lose someone.
Jargon and inferential distance are closely related, and you need to keep track of both together. People who are already thinking much like you are likely using the same words for the same concepts, and vice versa.
Also, even if you can talk specifically in technical contexts, learning to ease people into jargon and introduce lay members to engineering disciplines is a tremendously valuable skill to learn. As in a 4-year engineering degree and this skill is a quick way to get promoted to whatever position is in between management-types and engineering-types. It's really straightforward - just have enough technical chops to not completely embarrass yourself in a technical context, and learn how to explain engineering like your audience has an MBA, and management is going to want to talk to you about engineering projects rather than other people.
tl;dr - go ahead and use technical words in technical contexts, but try to do so in a way that those unfamiliar with the context can at least figure out what questions they need to ask.
Edit: I realise that I foolishly over-complicated and worded my question in a way that obscured what I actually meant. In essence, my question was: if we didn't have specialised vocabulary for things - say, in the area of rationality - would our rationality be hampered by our inability to be specific without long-windedness? Often words are created to bridge this gap when new concepts are created, so if we didn't have those words, would it take longer for us to understand or communicate and idea (to others or ourselves) and make it more difficult to be rational?
From the direction of the comments the general answer to my initial question is coming across as: "words are useful for communicating explicitly, and so an extensive or highly specialised vocabulary can be useful, if and only if the person/people with whom you are communicating understands those words". The internal understanding of concepts does not need words and thus a vocabulary.
I am curious about the relevance of vocabulary to rationality. I'm not talking about a basic vocabulary, but a vocabulary beyond that of the average, English-as-a-first-language adult. I believe there are a few correlations between intelligence as measured by IQ and vocabulary, as well as vocabulary and income(via IQ), but anecdotally I think it's fair to say that there are certainly people who are highly intelligent, but often irrational.
In reading through LW, I've come across a lot of new terms specific to certain areas of study, and I've had to look them up to fully understand that discussion of rationality - I assume this is probably true of most people new to the field, and applies to most specialised fields. Jargon is obviously useful within given fields where there is a need for detailed discussion of highly specialised topics, and helps one to discuss that area, but is it necessary to understand that jargon in order to practice in the field?
For example, I would think that a general practitioner would have trouble within his field if he did not hold the language to be able to specify what, in particular, was wrong with a patient, even if he knew what it was. Or could he not even be able to understand, say, that a patient was having a heart attack if he did not have the words for it? I suppose history might be a good indicator of this, or new scientific phenomena.
The field of rationality is one of both practice and theory - but if we didn't have an advanced vocabulary, could we still be highly rational? For example, my stepfather didn't finish high school, and makes up words like "obstropolous" (which I think kind of means stubborn and difficult to deal with on purpose) to say what he means, but he's also the type of person who, in a emergency, takes the most logical, rational course of action without panicking or doing something silly. On the flip side of this, he makes grand generalisations about races, religions and people while refusing to discuss the possibilities of individuality, or conceding any part of his argument to, well, evidence.
So do you have an argument for or against the need for an advanced or specialised vocabulary to be rational? Is it a question that's too vague, or with too variable an answer? I couldn't find any scientific papers on rationality and vocabulary, so I don't know if there's any data for or against, but I think it's an interesting question.
(This is my first LW article, so please be gentle but thorough with any criticisms you may have - I'm happy to improve or clarify!)