It's pretty simple if you don't under replenish
But I don't think you can over replenish since your using working strength developer right?
Well ...
One of the goals when using a replenishment regime is to reach an equilibrium that ensures consistency.
One of the things you are doing when you add replenisher is removing the same amount of used developer, including the byproducts of development.
Those byproducts are what causes the developer to "season" and are what gives the working solution in a replenishment regime its particular character.
The goal is to reach an equilibrium, so as to ensure that the amount of the byproducts in the working solution remains at or close to the ideal amount.
The danger is that if you increase the amount of replenisher that you add by too much, when you remove that same amount of used developer you may end up removing too much of the development byproducts, resulting in a working solution that "wanders".
It is, however, undoubtedly easier to get at least close to true consistency with a developer that is its own replenisher.