Optimizers around 5e #DnD say that a +1 is about a ~5% increase in success, but that assumes that the range of results is 1-20.
As we know the range of results in the game actually stretches from about 1-40 and the range of difficulties is 5 to 35. Neither of those would be a range of 1 to 20.
So all the arguments about optimization are about a ~2-3% gain.
