I think it depends on how previous information is brought up. Like robarrow said, if it's just to be argumentative then it shouldn't be mentioned, however if it's going to be helpful to the thread then I can't see the harm.
I think when posting we should remember that, in most cases, the OP has asked a question and so we should try to answer it rather than just stating a fact. If I may use Shores' excellent examples to illustrate my point:
In SitchA the OP is asking what should they do. Helpfully bringing up past info would be to say, "Could you take back the shoes you bought last week?", and it would be unhelpful to say, "Well, you shouldn't have bought those shoes last week."
In SitchB the OP is asking the same thing over and over even though they've had it answered. Helpful would be linking to a couple of the threads and saying, "You were given some good advice in these threads, have they not helped?". Unhelpful would be saying, "We've answered this question before. Why are you asking again?"