Modern day photographers really have become a bunch of whimps. Can't handhold a camera with 25 ISO Film pffft. I wonder how they did it before WWI and WWII. I've seen plenty of photographs made with handheld cameras ( Goerz Ango, Box Cameras, etc...) and slow glass plates or film and they were plenty sharp and shot under very different lighting conditions from brigh sunshine to rainy and foggy days. Those photographers didn't use super fast lenses either so how did they do it. I guess great technique.
Also grain is a minor reason for choosing slow films the bigger reason is the different tonality a slightly higher inherent contrast, etc...
As weird as it sound slower films are the right films for grey and foggy days with little contrast, the slower films just add a little necessary uumph that makes the scene come alive.