When I use stones like the Naniwa 12K or the Shapton 16K I occasionally get the feeling that they are not cutting uniformly. It's like the cutting grit plays hide-n-seek with the binder.

Now take slurry from that same waterstone and put it on a smooth hard surface. Suddenly the waterstone cutting grit is "between a rock and a hard place". It can't hide. So the cutting process is boosted. The cutting rate and feedback are much more uniform. Also, I don't enjoy lapping waterstones (lazy I think). With this slurry-on-UF method I don't need to lap anything (maybe someday).

I lapped and polished my Spyderco UF on one side. It is so smooth that it doesn't cut much at all. So the only cutting action I get with the slurry method is from the slurry. My guess is the effective or nominal grit produced with this slurry method is coarser than the grit of the slurry source. I say that just because the cutting action is faster.

I know some waterstones supposedly have slurry that breaks down into finer grit, but I don't know if the ones I use do. The scratch pattern from the slurry is very different than that produced by the slurry source stone. Instead of tiny uniform grooves it is more of a mist. So comparisons of fineness are difficult.

I just sharpen my own stuff, so I am not experienced enough to make any broad statements about this method. I just like the option of doing it when I think it helps.