I've worked at both kinds of companies (receipt and reimbursement vs straight per diem based on location) and much preferred the one that handed me my per diem as cash in an envelope before the trip started. Less bookkeeping on the company's end, and if I decide to be frugal on the trip for whatever reason I've just rewarded myself with a small bonus. Seems like everyone's incentives are aligned in that case.
These kinds of people like to think of themselves as smart when in reality they are just selfish.
Any action that cannot sustainably be extended to everyone else in the world should be considered suspect as to whether it's actually good.
This rules out lots of things that society accepts as fine. Although perhaps that's your intent.