Because claiming is a chore with no deadline. The receipt is in a coat pocket, the claim is filed at quarter end, and the month it belongs to has already been reported.
And because approval is often a formality — a manager approving forty lines they cannot possibly assess.
Route by budget ownership, not by seniority. The person who owns the cost centre is the one who can tell whether a claim is reasonable.
Set limits that the system enforces and exceptions that route higher. A policy that relies on people remembering it is not a policy.
Whatever makes the admin cost worth the control — set it deliberately.
Whoever owns the budget it is coded to.
Yes, reaching the invoice at the agreed markup.
Half an hour with your own data usually saves reading three of these. The guides will still be here afterwards.