Common name system has a lot of problems and confusions, because the name used in one part of the world is not understood by any person from other part.
As common name for apple in kashmiri is’chount’ in pakistan it is called ‘saib’ and so is the other parts of country and so by the many parts of world.
So un order to compensate the system a world wide union came into existance in order to facilitate the system of nomenclature. And so all the world would mean the particular name to particular thing.
To use common name is not sufficient because its vary from region to region , country to country even language to language.Common name is not valid throughout the world .
e.g: In Pakistan Alleum cepa is known as piaz ,gandha and many other common name in different region but this Alleum cepa in other country is known by different common name .
So, it is very difficult to recognize for native of one country to other country some thing .That why scientific names are given to common name which is valid through out the world.
Common names vary in different languages, countries, areas etc. so a common name might not be recognisable to everyone (even if it seems obvious), whereas a scientific name is universal. The scientific name also gives clues as to genus and other factors. It is also just considered more professional and makes you come across as more scientific, professional and knowledgeable.