I have most always run more oil than what others are doing with no bad affects. I'm sure there is a point with most engines where you gain nothing and may cause issues. I have been puzzled over the years why people try to get away with as LITTLE oil as possible. (?) Oil is cheaper than new engines.
I am not sure about anyone running as little oil as possible, but you can certainly get smoother runs and/or more power withe less oil, assuming your engine can safely handle it. And, you don't end up varnishing up the insides, taking your tenth of a thousandths fits of an AAC cylinder/piston and gumming it up with .002 of sticky residue.
More oil = more fuel viscosity = more fuel system drag.
Frank did not mention what engine he is talking about. Fox/McCoy/Johnson, can tolerate or require a huge amount of oil, and the Johnson used a sintered iron piston that *required* varnish/carbon buildup to seal. Clearances were super-sloppy. You RO-Jett AAC cylinder has clearances measured on the order of .0001" from the factory, trying shear castor oil with that creates tremendous drag. My engines won't even run reliably on Powermaster GMA fuel (22% 50/50) or similar mixes. It will run on Powermaster RO-Jett with 17% low-vis synthetic/5% castor), and it won the NATs on Powermaster "Sport" fuel with 17% total oil. I have been running the same cylinder/piston assembly since the 2007 team trials on, for the most part, 17% oil with 3/4 synthetic.
Similarly, we have abundant evidence that fuel line drag causes all sorts of funnies on a stock PA NVA with the usual Prather "medium" tubing on a range of engines, relieved by reducing the drag, or again, *running less or thinner oil*. We solved several independent "flame out" issues on PAs by running fuel with 17% straight synthetic. I have had to assist at least one person who, after running a RO-Jett 76 with a bunch of added castor (up to Fox Superfuel proportions) that could not be started in cool and humid conditions because it was so varnished up that the piston was sticking halfway up.
So, to answer the question, every time we have tried running less or thinner oil, or reduced the fuel system drag, the engine ran better, or in some case, was necessary to make it run at all. I can't tell anyone else what their particular engine and fuel system setup needs, but we are trying to compete with what amounts to stone knives and bearskins, so you cannot afford to give up any sort of performance or run quality/run control. I have seen exactly zero ill effects in terms of wear down to - so far - 17% total oil, straight SIG or Powermaster RC sport fuel straight out of the can, or SIG Syn-Power.
That's why.
Brett