It's diminishing returns right after you have fuck you money to live in reasonable luxury afterwards, e.g. you can travel as much as you want, order food in, buy latest tech widgets etc without having to ever work again.
For me it was realising that my total outgoings (after everything) are now 33% of what I earn every month and I have enough in savings to cover at least 2 years and every month I work adds two to that.
It’s not fuck you money in the I can retire sense but it’s more than I’ve ever earnt/saved before and very liberating.
Just got promoted so pay is going up again as well.