I cannot get any fully scientifically tested [with proper controls] results stating that staining is either good or bad. Most threads that try to thrash that out get into flame wars and I stop reading them.
This is what I found when researching a question on another thread. When you try to research staining developers what you find is speculation and personal bias with little real information. For example, on this thread 5 people say to place the negative back in the used developer and 3 say don't do it. None of the 8 people offer any scientific basis for their opinion.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.