I initially formed this opinion on stones that didn't come with a pre-load of oil or boiled. I always shied away from oil because I felt it was too messy. I also noticed over time my stones would slowly degrade in performance - this being used with soapy water or dry. Lapping with loose grit would restore them and then a slow decline. Hmmm. tried it with oil and low and behold, the stone surface looked and felt smoother and more uniform after use, and my ability to cleanly nip the burr without a chase improved - better abrasive potential at lower pressure = no glazing, sharper abrasives and for me a sharper edge off the same surface. When I used water based materials I could always tell where the wear patterns were - used with oil the entire surface looks and feels the same after use.
This effect really kicks in on my SiC stones, but is apparent on my AlumOx as well. I use enough oil that the stone has a film on top. If it dries out in use I'll add another few drops to keep the junk suspended unless I'm down to the final passes. If I'm still grinding, there's still oil on the surface. On longer jobs I'll add some oil, agitate with fingertip to suspend all the junk, wipe with rag, re-apply and keep going. Overall I find the oil to create less mess thana lot of water. I also use a relatively short scrubbing pass, so the oil tends to stay put. If I were using long sweeping unidirectional passes, the oil would be squeegied off a lot faster, so some of this must play a role in perceptions.
I boiled the oil out of my first India stone and used with soapy water as was my habit at the time - I also boiled the oil out of my Crystalon stone when I first got it. For a while, after I started "experimenting" with oil, I was bouncing back and forth between soapy water (no need to boil the old oil out if there's soap in the mix) and oil. Noticed the thing almost immediately became discolored. Bought another one and used it with oil without boiling the pre-lube and the surface is always like new and no discoloring = no loading.
I can and have used my SiC stones without oil, but never by choice. I used to bring a small Norton SiC puck when camping and just use with water - works fine, but if I'm around home I'll use it with oil whenever possible. In my opinion, there's a reason all these large mfgs recommend and sell honing oil for use with their vitreous stones, and none sell soapy water additive or rubber blocks/brushes, etc for use with their stones, it isn't because they bank a lot of $ selling small cans of oil.
Again, it works either way but for me there's no doubt which works better.
