That's also not true. A poll that is consistently biased in favor of one candidate, but is otherwise very precise (that is, less noisy than others), is actually significantly more useful than a poll that has no bias but very low precision (swings wildly due to noise). If that's the case with this particular poll, then it is very meaningful as long as you sufficiently account for the bias.
I agree, this is very useful for seeing trends due to them pollling the same people over and over. So the question is how big the Trump bias is. Trump was ahead by 7 in this poll, but he was arguably never ahead by more than a point or so based on polls in general. Would it be excessive to give this poll a Trump +6 house effect? If we did that then Clinton would be at +7 right now, which seems fairly close to the overall polls right now.
