Bromide (and iodide) will be released as the films develop. That bromide will have an affect on further development. By adding bromide to the developer, it will minimize/supress the effect of the released bromide. It will slow the rate of the development reaction as there will already be an excess of reaction products present in the solution.
Developer exhausts as well. And that will slow the reaction as well as have effects.
I've pointed out in other threads occasionally, I think it is the use of hydroxide that makes Rodinal such a popular choice for stand development. Using hydroxide as the only source of pH gives an interesting set up that most film developers do not have.
Hydroxide has no buffering power. When it is neutralized by acid, it simply turns to water, which does not buffer the pH. You don't get that with carbonate - when it buffers, you get bicarbonate, which can combine with excess carbonate present and form a pH buffer. Borax and Kodalk will buffer with the addition of acid as well.
As the hydroxide is used up in the reaction, the pH being unbuffered, will drop rather quickly. So even though the pH of Rodinal is nearly pH 14 in the stock, and about pH 11.5 when diluted 1+100, it will probably be at a much lower pH at the microscopic level in the film.
I'm sure PE can speak to the actual micro pH levels that can be measured in emulsions with the right kind of micropH probes.
At least that's my understanding.