They are the people who can be used to explain everything or cinch any argument.
"They say you should eat right and exercise."
"They say you should look out for yourself because everyone is out to get you."
"They say you should look out for others, especially those who are less fortunate."
They are not always right. They are just a convenient way to prove a point. The best part is that no further proof is required if you use "they".
"They say we need to refresh our corporate website."
On the last point, THEY are quite right this time.
And it is time to do something about it.