For lots of economy/finance-related data, usually there is an expectation, and then people will compare the real data (when coming out) with the expectation, to see if it beats or misses the expectation.
Just name a few, the unemployment rate, company's earning, crude oil reserves, and much more.
The price of related product (stock, etc.) usually changes according to beating/meeting/missing the expectation.
Why people like to set an expectation beforehand? What's the usage?