I see lots of comments on back-end savings that might not be apparent up front.
The problem is, my team has a tight travel budget like most others I'm sure do. If I have a $1,000 budget for a trip, I can't say "well this ticket is $600 but the company as a whole probably saves money over this $400 ticket."
My manager and his manager (who approve travel) see $600. So I don't get that perspective that a lot of people are sharing here.