"Clear and understandable" to who? Communication in general, and writing in particular, usually has a target audience. If your audience can grok[1] it, go for it!
As an extreme example, you cannot write a "clear and understandable" PhD thesis in Linguistics while avoiding five-dollar words (to borrow the term).
I think XKCD's "up-goer five" is a suitable counter argument against words that are too simple to clearly communicate complex ideas succinctly. Jargon has its place in language.
1. Meta-excercise: attempt to use the word 'grok' in casual conversation with a non-techie.