It means like don't over use it or don't under use it. Use it for when you need it and when its important rather then use it for something that doesn't matter.
Answer:
Metaphor
Explanation:
It is not a simile because it does not use the words 'like' or 'and'
Answer:
The answer is the first option
emigrate should be immigrate
Explanation:
Emigration corresponds to the act of leaving the country and the place of residence, while immigration refers to the act of entering a new country from another.
In this case, people emigrate out of their countries to immigrate to the United States in search for better living conditions.