It may indeed serve a useful purpose to have a wandering mind, but as the article points out "the hallmarks of many forms of mental illness is a preoccupation with one's own thoughts", i.e. perhaps the issue is the extent to which one's mind wanders. Not all minds wander equally.

Personally, my wandering mind has been my greatest strength and my greatest weakness (anxiety, worry, jumping to conclusions, all or nothing thinking, etc.). I spend too much time in my head and not enough time grounding myself in reality to the point where there is serious disconnect in my awareness and mindfulness of situations (which has caused all kinds of serious grief in my life). Meditation has been recommended to me numerous times, and based on this article it looks like it's something I want to explore.