I screen hundreds of resumes a week when hiring. I know this very well.
Hiring the wrong person can easily be a net negative to the team. Hiring too fast and desperately hiring anyone who applies is doubly bad because it occupies limited headcount and prevents you from hiring the right person when they become available.
Building teams is a long game.
So if you don't have a job opening posted on the day they're sending out applications, you may miss your shot to hire them.