This should slow down oxidation in developers, just likel it does with food. The cavaet here is that it can cause some componemts of some developer to crystalize out. They may not go back into solution until you re-heat them to the original mixing temperature, and depending on the mixing sequance, they may not even go back into solution then. I do sometimes keep colour developers for E6 once mixed in the fridge between uses, though, if I know I will be using them again in a week or two.