Of course there will be some who have odd combinations, who don't feel as if they are compromising on tyre choice, but it never makes it best practice, definitely does't follow the advice or recommendations of the experts.
You may not even feel there is any defficiency, but another driver in that same car, may feel it isn't what it ought to be.
Mixing tyres has always had this sort of reaction. I remember reading a guy using 4 odd tyres on a Ford Focus saying it made no difference than having 4 the same, debating it with another guy who had lost the precision of his Focus, by just changing brands. We don't all come from the same place when driving.
We know there can be major issues on something like the E46 330ci when mixing tyres, front to rear. Again some say it makes no difference to the car, but others have found the car becomes near on dangerous, just by having two odd pairs, even Michelin PS1 and PS2 didn't work together. Get a bit of suspension wear in the mix and that can completely change the tyre mix equation.
Big subject, but the official advice is clear, don't mix run-flats with non run-flats.