For credentials it probably does not really matter.
But in principle: when working on bigger projects I found it advantageous to have separate configuration file - I am not familiar with the config package - as either a text file or an entry in codebook table in database.
One advantage I mentioned already is version control - it is difficult to version control the contents of your renviron file; much more easily done with a small text file.
Another advantage is that you can easily have the config file temporary in nature - say if you have parameters governing a complicated migration. You have a version for development, another for testing (perhaps different ones for several rounds of testing) and then a production version, which you later replace with a "clean" production code in a later release.
For getting rid of the no-longer-required parameter it is easier to remove a file / entry in a codebook database than deleting an entry in renviron file.