It filters out the people whose ego won't let them take the test.
Re:Show HN: Coding Interview Practice
by krainboltgreene on Thursday March 27, 2014 @07:39AM
(#7479704)
And people who don't think tests are a good start to a relationship between an employee and a company.
And people who are getting better offers at better companies.
You'll never know.
I'm not sure that shows up in hours of interviews either...especially when most (all?) of that time is spent on "technical assessment"