Actually, there is a lot more to what Michael wrote. One role of sulfite in some developers is said to regenerate developing agents like hydroquinone, which in turn regenerate the other superadditive agents like phenidone. In this mechanism, lower concentration of sulfite may drive the result to higher accutance (by promoting the local exhaustion of developing agents) but has little to do with solvent effect or physical development. By the way, what physical development usually means is deposition of dissolved silver halides on developed metallic silver grains, but not the dissolution part.(posted 8194 days ago)But these are rather controversial topics and I recommend not to try to generalize too much by putting together and stretching what people say.