When does anchoring improve our judgement? Anchoring is the behavioral pattern where the first piece of information we receive about a situation is what all other data points are compared to. For example, the price of the first menu item we see at dinner, the degree of physical pain experienced when exercising, or perceived positivity or negativity in an interaction with a person -- whatever our first experience of these contexts might be, we're likely to view all information received afterward as being either worse or better than those initial impressions. 

When I’ve read about anchoring, its been discussed as a cognitive bias, and it appears to be viewed as a huge blind spot in human reasoning. But if this is such a strong tendency, it must serve us in some contexts (or have served us at one point in time).

So, does anchoring ever improves our judgement, instead of deprecating it?
The underlying cognitive process that produces the "anchoring bias" in decision-making is the same one that produces the "primacy and recency effect" in learning and memory. Your attention is drawn to novel, salient and recent stimuli, and are more likely to learn about and remember more about the first example of something and the last (most recent) example of something. This means that you are able to learn and adapt faster than you would be able to under an unbiased learning method; in some situations, you can effectively generalize from only one example (you only have to touch a hot stove once). For real-world situations, this speed of learning gives you an enormous advantage. For an additional set of real- and abstract- cases, you will have the opportunity to revise and improve your anchored estimate with small or zero penalty. In all of these cases, having a fast-learning, pattern-seeking heuristic-based cognitive system beats a slow-learning but unbiased cognitive system (which you still have, running on top of the faster system).

It is less powerful in cases where you are doing abstract numeric reasoning (for which there is no plausible estimate) or are negotiating competitively with another person who is faster/better/more informed/able to deceive you through anchoring or other techniques. In these cases, the drawbacks of the system predominate.