I don't like to see my vault dwellers be unhappy. Does it affect anything that I should be worried about? Give me suggestions on how to make their happiness go up.
Over all Happy Dweller make production faster. If you's average rate of happiness is 90-100% you will have the benefit of Food, Water, Power + 10% reduce in production time . This benefit will be reduce 1% for each 10% of average happiness.
The easiest way to booth the happiness is to "get laid". The dweller who "get laid" will have 100% of happiness.
There are some reasons that make your dweller unhappy include: lack of food, have a dead body in the room. If you remove these factor the happiness will raise again.