It is usually an indicator that worse will be coming. It also may exist at the moment but you just haven't noticed. It might show its ugly head one day as you are trying to pass a car at 60mph. I have noticed that most of the cars I see with that code and a AMM problem have flat spots in their acceleration, eventually up to the point that the car falls on its face with a sudden full throttle acceleration.
There also is a more technical/economical reason. Your car reaches that code when its ability to center the mixture control range is reached. This at first doesn't matter to anything. Whether it has more ability to correct lean than rich doesn't matter as long as it doesn't need that extra correction (the sudden passing of a car might find one of those times). Eventually it is likely that the lack of ability to center will mean that it doesn't have the ability to maintain closed loop control. This still probably won't be felt except in those special conditions, BUT, your catalytic convertor will know. It is absolutely imparative that a modern cat see an exact average mixture that equals the precise chemical portions to effect the burning process with nothiong left over. Excess hydrocarbons, which happen anytime control isn't maintained, will ruin a cat in a short hiway trip.
Bosch Master, ASE Master, L1
33 years MB technician