If I really stretch it I could see that maybe if your crankcase contained some light distillates and the vapors were getting into the combustion chambers they could make the engine run a little differently. It is a stretch.

Years ago I did a similar flush job on an engine that had little to lose. Don't know if it did any good but the engine ran a long time afterwards. Don't remember what I used, probably diesel. Seems like it was right before I dropped the pan and valve covers and had them dipped while off. All in all it removed quite a lot of crud from the engine.