In a balanced person, the functions play off of each other. Some overlapping concepts that I recall from different places that seem to represent a lack of balance:
- One function excessively dominates a personality or, rather than being used as a compliment, the other functions become enslaved by it.
- A person's auxiliary is not sufficiently developed to counterbalance the dominant function and/or the tertiary is overused.
- The inferior function excessively erupts or dominates in someone's day to day life (see Quenk).
- One or more of the shadow functions move into an area of prominence, usurping the auxiliary.
There was also a fascinating thread here about how unbalanced/unhealthy individual's Ennegram type (the defense mechanisms) overrides their MBTI type, which could indicate that somebody is out of balance.
Finally, I think Case Study #3 in the the link in the following post gives a great example of somebody who is not balanced .
Edit: But I am loathe to ever assign a label of being unhealthy because I think we all are in certain ways.