Job posting - the automatic feeds to Indeed alone saved the company thousands of dollars (we couldn't get it to work before we implemented the ATS) and filled lots of jobs.
The implementation of Jobvite (along with a comprehensive upgrade to our entire recruiting program) allowed us to cut time per hire drastically, drop cost per hire from ~$8k to $2k per hire, almost entirely eliminate agency use and get the agencies we continued to use under control, improve manager experience, exceed our staffing plan, and drive a higher quality of hire because recruiters had more time to focus on the value-add parts of recruiting.
The RFP had been started prior to my joining the company and the final decision was down to Jobvite and Newton. Jobvite seemed like it would have the ability to scale further and meet more of our business-oriented (vs just recruiting) needs.
If Taleo had been in the running (they were due to their recent acquisition by Oracle at the decision point), they probably would have won the RFP.