It's a euro kinda thing... :-)
Actually, the presta valve is 2mm narrower than the schader valve we are accustomed to, here in amerika.
What that gets for you, is less of an intrusion into the rim, hence a stronger rim, especially for the skinny road racing tires and such.
...So, they ARE a good thing, for the right application...
Personally, I don't feel skinny tires have any place on a motorized bicycle because we are generally moving faster and encountering pavement variations at a far greater speed than most pedalists. We need the protection of a fat tire. ...and the bit of suspension they afford.
Now if you are building a motorized bicycle for a speed record on a closed course with a great surface... well, I'd have a skinny road racing tire!
When he made his run at Bonneville, Auggie was glad he had chosen a medium width tire because of irregularities in the salt,and cracks, that he says would have swallowed a skiny tire!