I learned that from Jeff (hopfen) who learned it at Sierra Nevada beer camp, so there's at least one major pro brewer that needs your expertise.
I have found that it helps when there is a lot of fine particulate on the surface of the grain bed.
Its interesting that you mention SN since the firm I work for is providing engineering services to both the Chico and Asheville facilities. I'm pretty sure they don't cut or rake the grain bed in a 200 bbl mash tun. They are sort of big. But the description you and others provide, make it clear that the purpose of the cutting is not: "to prevent channeling", but to improve flow through the bed by disturbing that surface layer. That makes perfect sense.
I mash with RIMS and the flow rate through the bed during mashing is far higher than when I'm running off. I've never seen a layer of anything on my mashes. I wonder why regular mashes present this. Do most brewers have this layer on their mash?
Given the real purpose of the cutting, many shallow cuts through the surface of the bed would be most effective.