More money = happy workers, unless of course, you don't give them money, but also other economic benefits that are equivalent to money. I'm not seeing the nuance.
If you don't have to pay for child care because you can just take off the time to pick up your kids from school, you are saving money your job otherwise forced you to spend.
Being forced to commute at peak time costs more - on a retail salary the difference between a peak and off-peak ticket can mean that the first hour or two of working is essentially pointless, as you're just paying back the cost of getting there in the first place.
Having to pay an extra surcharge to visit the dentist, because you can only go on a Saturday because you need to be at work other days. Flexible working would allow you to just take the Tuesday off no problem and go when it's cheaper.
I'm sure there are lots of other examples that apply to different lifestyles.
hours with your child aren't fungible. you can't pay the babysitter to go see the dance recital for you if you want to be the parent instead of the babysitter being the parent. all the money in the world isn't going to make up for missing the soccer game where your kid makes the winning goal.
Well to be pedantic, with all the money in the world you wouldn't be working for Ikea and the problem wouldn't exist so really that's a problem also solved by money...
Generally though higher paid employees tend to have more sway within a company structure and likely don't need to miss these important events, the win here is that something that was generally true for mid management up for most companies now extends down through all the ranks.
You can manage things in your life when they occur instead of spending money to displace them or risk losing your job because of them.
In another way, if you present a worker with the option between two jobs with the same hourly rate, one having flexible working hours and the other not, which would expect to be more likely choice? You can then measure the value of this choice by changing the hourly rates between the two until you see changes in outcome and you would be able to estimate exactly how much "more money" it appears to be "worth."
More money = happy workers, unless of course, you don't give them money, but also other economic benefits that are equivalent to money. I'm not seeing the nuance.