Most of the complaints come from a matter of taste, however you'll find some who dislike the New American Bible because they believe it contains doctrinal error or ambiguity. This is the case with most translations. Catholics can disagree with certain things like the choice of translation for the Bible in liturgy, however the decision of the bishops should be respected and any disagreement ought to be constructive. I can't cite specific examples but perhaps someone who lives in the U.S. and deals with the NAB often could provide some? Wikipedia
may also help. I'll note that I don't really care for the NAB myself, I appreciate "archaisms" and like translations that use them personally.
The New Jerusalem Bible I'm not certain on, however the New Revised Standard Version I do know. It is the translation currently in use in Canada but is not
approved for liturgical use by the Vatican. It makes use of "inclusive language", which poses problems in many parts of the Biblical text. Wikipedia also covers this
and probably does a much better job than I could. Apparently
the New Jerusalem Bible falls into this as well, that I didn't know.
The purpose of different translations is simply because the original languages possess words that are difficult to translate or have no English equivalent. Mostly it is a matter of taste however there has been a good amount of translations that are doctrinally incorrect, false in some form, or problematic. For instance, Martin Luther inserted words into his German translation of the Bible that changed the entire passage.