Back in the '70's I read something from an insurance company that indicated daytime accidents were significantly reduced by using the headlights in the day to be seen better. I was driving a Saab 99 LE at the time, and I noticed the headlight switch was connected to the keyswitch - I put 2 and 2 together and realized the intent on Sab's behalf. I started driving this way, and every day dozens of cars would flash their lights at me, thinking I had "forgotten" my headlights, and that they were saving me from a dead battery situation!
Years later, driving in Sweden and Denmark, this made much more sense, as the sort of semi-dusk that prevails there through half the year easily explains why all cars there are wired this way, and everyone drives with lights on all the time.
I believe this use is much more pertinent in places like this than say southern California, where it's blazing sun every day - people will hardly see your lights - nevertheless it is a good practice to bear in mind. In fact, it is now the law in Italy, and will soon be in France as well.
The reason the DRL position doesn't allow the high beams is that you may not be aware you have them on (you cannot se the effect of course, and the little light on the panel may not jump out at you in daylight conditions eitjher) but it could still be aggressive to others, particularly as dusk approaches. The "flash" function remains available as this is how Europeans get others' attention - not only to pass them, but for any reason. Sometimes it's used to say "I see you, and I'm letting you go ahead of me". Other times it means 'Look out, I'm not stopping". You have to understand which is meant!!
Now I notice in New England, where everyone used to flash at me for driving with my lights on 30 years ago, many many cars are driving this way, and no one sees it as odd any more. At present, I always drive this way, unles it is a very bright sunny day, in which case I turn them off and probably save a few drops of precious fuel.
GF