As someone who worked with a per diem expense account vs a non per diem expense account, I can tell you I made a shit ton more money on the per diem. I’ll give you a for instance. With a per diem, I eat 2 meals a day, and I eat cheap. Let’s say the customer provides lunch during our workshop and then I go get subway or something for dinner. I spent $10 on food that day and I get to pocket $90 of the $100 per diem. Or, I have a much nicer meal on my non Per diem account for dinner. I don’t claim breakfast because I didn’t eat it and I don’t claim lunch because it was provided. So now I have $50 dinner and I walk home with $0 and the company saves $50. Of course I could throw in fake meals for less than $20 for breakfast and lunch and wind up with ~$40 cash, and the company still saves $10, but that, I agree, would be stealing. I picked $20 in this case because my current company requires receipts above $20.
Anyway, usually it’s cheaper for the company not to offer a per diem. Though I loved those per diem trips when I was traveling with a sales person and they picked up all the food bills, then I got to pocket the whole per diem every day. Oh, and final note, the company’s I’ve worked for offered the per diem for daily expenses, airfare/mileage, ground transportation and hotels were all handled outside that.