With respect. It’s actually the only way to accurately and simply apply the correct weight penalty to the aircraft for all enroute possibilities including drift down, otherwise you will not be in compliance with the regulations governing CDL use so to suggest its not relevant is bonkers. Having a lovely flight plan but not tell the FMC ? How is a performance supplier going to help you with the engine failure off the designated route due to weather deviation when your weight is not the same as the flight plan ? The FMC will do it perfectly but only if you tell it about the CDL first. Regulations are actually there for practical reasons not the other way round.