If you describe someone as well-balanced, you mean that they are sensible and do not have many emotional problems.
a fun-loving, well-balanced individual.
一个风趣且明智的人。
If you describe something that is made up of several parts as well-balanced, you mean that the way that the different parts are put together is good, because there is not too much or too little of any one part.
a well-balanced diet.
一份均衡的饮食。