Most expense tools optimise for employee convenience. The best ones also optimise for finance-team trust. The difference: policy enforcement at submission, not rejection.
The classic failure mode of an expense system is soft enforcement. An employee books a business-class flight in violation of policy; the system lets them submit it; finance rejects it after the trip is already taken.
Hard enforcement at submission time is uncomfortable but right. The fine-grained approach: block the submission, show the policy violation, let the employee override with a mandatory reason that routes to manager + finance approval. Trend the override rate.