Again, it never fails to interest me the differences in perception. I heavily rely on tactile feedback when sharpening, and find it to improve with use of oil. I even apply a very thin film to my diamond plates.
I also find the debris that would otherwise potentially clog the stone by laying on top of the surface, to be largely lifted off in the oil. On waterstones, a mix of binder and water is used to float the swarf. Water alone is not as effective in this regard though is capable of holding some swarf in suspension, all it really is doing is preventing it from being ground into the stone too much.
By floating it, the stone surface is less encumbered and grinds faster and cleaner. The bit of floated swarf and abrasive also produces a mild lapping action that aids in keeping burr formation to a minimum. If the amount of debris suspended in the oil is enough to impede grinding (considering some of it isn't even resting on the contact area of the hone), why would we expect it to have no effect sitting on the surface of a dry hone? I find it does make a difference and has to be managed somehow for best results, oil is a convenient medium and also recommended by the manufacturer...
Only on very coarse stones do I find the mix of swarf and oil to slow the grinding process, and these stones have so much space between abrasive points the debris has plenty of low spots to fall into. Unit pressure is also very high which encourages the abrasive to break down sharp. As the unit pressure decreases as grit size decreases, tendency to glaze will increase - oil tends to keep the abrasives sharper at lower pressure.
It isn't a mystery or hoodwink, just properties of abrasives and how they interact with steel.
The swarf has to go somewhere - either it sits on the surface, falls into the gaps if possible, or is removed somehow - how often depends on how much debris is generated. Floating it away is a good mechanism. Consider how much better a hacksaw or drill bit cuts through metal when used with oil as opposed to dry. It doesn't impede stock removal, quite the opposite. Prolongs the life of the saw blade/bit as well.
On some abrasives, oil or water aren't needed. Compare a file to the saw/drill bit analogy. On wet/dry sandpaper I find use of oil to be a mixed blessing in that a slightly finer edge is had, but is tough to get all the swarf off the surface. If allowed to build up/dry out, the swarf/debris impede grinding. Likewise with water - yields a somewhat finer edge yet the swarf and debris seem to impact into the surface more and reduce lifespan. Even when used dry, if the swarf is allowed to build up the paper will still feel very rough, but grinding will slow considerably unless the debris is removed somehow - I use an eraser or synthetic wine cork. If it isn't cleaned regularly the life of the paper will be dramatically reduced, yet even then some plugged wet/dry will respond very well to a few drops of oil and continue cutting once the swarf is floated out of the paper.
On lapping films, a small bit of oil makes a huge difference in preventing the film from loading compared to water or dry.
On stones like Juranich's vitreous stones, the composition is designed to break down and be used dry - BTW they work very well with oil too.
I don't believe there is a blanket answer, but like everyone else I know what I have observed and that's what forms my opinion. I encourage folks to try both.
