Solid fills are preferred, hatched fills are basically a thing of the past. (Page 8)
I clearly see the advantage of solid pours over hatched pours: overall better thermal and electrical properties.
But then, why were they so common in older electronics?
Actually, I still see them on some relatively new products¹, so I don't know if it has something to do with industrial etching procedures back in the days, or if it has something to do with EMI.
¹ For example, on a cheap phone charger I took apart the other day.