An ATS is the spine of most recruitment operations. It tracks contacts, roles, conversations and outcomes. ATS systems handle workflow well, memory and context poorly. The data sits in the record, but the reasoning behind it (why this candidate, why now, what to open with) lives in the recruiter's head.
For specialist recruiters, the ATS is necessary but rarely sufficient. The signal that decides whether a placement happens (a new paper, a public POV, a strategic move) lands outside it.