I think of grain on greens as the putting (and chipping) equivalent to playing shots in windy conditions...who of the grain haters would also say they think wind is undesireable?
That's a perfect sentiment.
I grew up on a little nine-holer in northern Minnesota, and recall having some putts on those greens that were so fast you could barely keep the ball on the putting surface. In recent years I have had experienced supers tell me there's no possibility that those greens could have been that fast--which is probably true. It was, after all, 40+ years ago.
But now I realize that what I remember is the grain. On bentgrass, grass tends to lay down with the water flow, and those greens all had enough slope that there would have been some grain to accentuate the speed of downhill putts.
From a strategic golf standpoint, it made it even more important than usual to be below the hole. It also meant that uphill putts required a firm, accurate stroke.
It's not accident that Tom Watson never won in Florida until late in his career, or that John Huston never won on bentgrass.
K