One of the worst things a quarterback can do is to check down on third and long. Yes, sometimes a receiver will heroically make it to the sticks, but in general, if a quarterback doesn’t throw to the sticks, they are often (but as it turns out, not always!) conceding a punt, which is the equivalent of conceding a turnover.
Every year, Football Outsiders measures a QB’s propensity to check down at the worst possible time through the stat of ALEX (Air Less EXpected, named in honor of Alex Smith). ALEX is a measure of whether or not quarterbacks throw to the sticks on third down.