Comment by bluGill

The problem with duplication it is hard to spot and fix. Converting liters to ml or quarts isn't hard, but the factors are different, and there is also other units. If you only do a few of these isn't a big deal, but if you suddenly realize that you have tons of different conversions scattered around and you really need to implement a good unit conversion system it will be really hard to retrofit everything. Note that even if you have a literToml, Literto Quart and MileToKm functions retrofitting the right system will be hard. (Where I work we have gone through 4 different designs of a uber unit system module before we actually got all the requirements right, and each transition was a major problem)