Miele seems to automatically run a prewash on the W1 machines if you select heavy option on the soil level query for the auto dispenser.
The only time I could see it as being useful is if the clothes are actually soaked in something that's going to wash back into the water, like maybe something absolutely covered in mud.
I find it genuinely useful for muddy football gear. That's about all though. I mean what else gets THAT dirty?
I guess maybe something like a completely messed up table cloth or baby clothes that have been absolutely covered in food or .. worse or very messed up work overalls perhaps?
It's an option that's still available on a lot of European machines, and a bit like the boil wash cycle, I think it's very rarely used.
From an environmental point of view, it seems like a waste of resources. I've never seen a front loader (certainly any I've owned) fail to do a good job if you use the right detergents and a good wash cycle i.e. not the 15 min quick wash or something ridiculous.
I definitely remember using self-service commercial machines in a laundrette in London in the mid 2000s that all did a prewash as part of the standard cycle, which was very short, very splashy and very deep. Definitely cleaned the clothes well, but it was using a lot more water and chemicals than a typical household machine.