It is interesting how something considered harmful can have beneficial effects. In this case reintroducing wolves could control the deer population and help the re-establish some of the Caledonian Forest.
There was another example I read recently: the Indian Vulture Crisis[0]. Apparently the vulture population in India has been declining dramatically. I wouldn't have thought vultures were particularly good, but their declining population has led to all sorts of significant issues such as an explosion in the number of wild dogs and the spread of disease. It has been traced to the administration of an anti-inflammatory called diclofenac to livestock.
Nature has many complex interactions.