The subject of "best value" is worthy of more attention, specifically with how this idea works in practice.
There is a tendency to try and keep control of travel spend simply by saying "the cheapest" - there may be a qualifier which allows the use of the premium or business cabin over a certain length trip, though essentially "cheapest" is still the main driving criteria.
One of the precepts of best value is thinking about what a journey may achieve in terms of your company's return on any trip. That is, the potential income (or income risk) any trip may generate (or, of course, ameliorate). A senior person glad-handing, for example, could be set against the lower-ranked person, sent to oversee the fine print of a contract.
I need to send a manager to Hong Kong, from London to finalise a very important, significant-sum contract. Just need a day or so in Hong Kong. Well, the rule is "the cheapest" so what do we do? We send the person on a 42 hour, 2 stop trip there and then bring him back on a two stop, 25 hour trip. Cost? £473.00. Great saving! Well, is it? Your person arrives in the sort of state you would expect after 42 hours and 2 stops. The resultant mistakes made cost your firm a figure in the upper £50,000 region.
The cost of sending that person on an 11 and a half hour, Premium Economy direct service would have been £866. (This is an actual example, by the way... so you will have to trust me on this one)
Now, I am not saying (all) the mistakes would have been automatically avoided; what I am saying is that any person sent on a 42 hour, 2 stop trip cannot be expected to hit the ground running. There was no time to recover. Given the importance of what was to be achieved, the purpose of the trip should have had much more bearing on how that trip was executed. Setting policy using cost as a main driver or using length of journey or seniority should allow leeway for "purpose of trip" and readers of my occasional writings may remember that I have, in the past, suggested that you look carefully at a number of past travel events and consider the return for your company, from each travel event.