Joanne probably had to field some "sorry, this can't be expensed" situations, and/or those were reduced because people knew another human was doing the work and they'd get called out, trying to game/abuse the system was less or just naturally discouraged. That was high trust, by both the employee and by Joanne.

With the employees needing to use Concur directly, there's a tendency, since there's a diversity in how each employee will handle the specifics, to try to "save money" by denying reimbursements for any random violation, making sure all i's were dotted and t's crossed. The automated system itself encourages this because it's so low effort to deny and send the expense form back, potentially wearing down the employe that they just give up. Joanne could avoid all that at scale because there was little/no diversity in how expenses were handled. If an i needed to be dotted, she could handle it, and she knew all the i's that needed to be dotted across all expense reports.

I currently have someone to handle my expense reports who sits in front of Concur for me! And that person routinely asks me for specific detail without me having to mess with Concur at all, things like "who was at this dinner you gave me a receipt for" or "I can't find the receipt for this company card charge".