They are called day running lights, as the cars originally came from Sweden where this is normal. We have had Volvos for years, and it's always an advantage to see another car with lights on, as certain colours of car disappear into the background. With lights on you're more likely to be seen by others.
In our older cars we could take a fuse out to stop French drivers in France forever flashing us, but I don't think that can be done in the modern Volvos - unless someone knows different?