Mercedes specifies a spray and pressure test of the injectors every 100k. Some cars have never been done. If fuel milage is pretty good and engine runs basically well just a cleaning with diesel purge will do no harm. Some people seem to forget that injectors are a periodic maintenance item.

They can and will wear with time and milage. Needless to say burning only real diesel fuel will prolong their serviceability. I tend to primarily only fuel at very busy diesel pumps. This goes a long way towards getting less water and other fuel issues. Even once bitten will usually will make a person adopt this habit.