According to the supplemental guide, a selection expert uses tests to choose which applicants to hire because:

The EEOC says that organizations cannot legally hire new employees randomly

It will usually be cheaper and easier to know who the best employees will be before incurring all of the expenses of hiring them first

I have a professional obligation to buy and use as many commercially$-$available selection tests as possible

The law says that I must use selection tests to make hiring decisions