>>But do YOU know the good reasons?

Yes, of course I do.

Generally, mechanics are not experts in vehicle dynamics. Yes, they spend all day on the tools, but, their experience of engineering of vehicles in its broader sense is extremely narrow, and their advice to deviate from spec is usually ill advised.

As per Craig's post above, setting the tyre pressures in accordance with MB specifications is the right thing to do.

>>I would be very sceptical.

I agree.