'Just' is quite rightly included amongst the C2 wiki list of Alarm Bell Phrases. It's a dangerous word that should be used as sparingly as possible. As a developer, it's a word you hear far too often: "this will just take a few days", "it's just a couple of web-pages", and of course the ultimate: "it should just work."
'Just' is a vague, almost condescending diminutive. Nine times out of ten, it means this:
I do not know, but it is in my interest to estimate optimistically.
Generally, you'll find that if you have a definite idea of the size of something, or the amount of effort required, the word 'just' quickly vanishes from your vocabulary. Not because the thing is necessarily large, but because even being certain that something is small removes the need to qualify its smallness: it becomes what it is, no more, no less, no 'just' required.