Its important to be aware of people's feelings because emotions are very powerful, that's why they made the expression words are stronger than fists.
One example of the unhealthy way to express feelings would be: say for ex your father got a job but requires the family to move to another country, u have been living there your whole life, made friends, maybe u are dating, or etc, and now u have no choice but to go with the family, the unhealthy thing to do would be to NOT speak up of your feelings to your parents, u don't know the result, it could be good or bad, words affect people in different ways so your parents may not move, and its unhealthy to bury your emotions like you bury trash in a trash bag, because the deeper it goes, the more the smell gets stronger, so same with emotions, the more u stuff it the more u are honestly hurting yourself. And u can affect someone by honestly taking out your anger or sadness to other people it can hurt them emotionally or physically.
Second example: say for example you are dating and you are in love, if u have feelings for the person you are dating it would be good to express your feelings by talking to the person and telling them how u feel, because if u don't, maybe that person wont feel the way u feel about him or her and will maybe have other feelings for someone else so it would be healthy to express it and it would be positive because its like carrying a TON of emotions on your chest and arms, but now you lift it off and its gone.