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.
Same plants as well as animals have different names in different countries as well as within the country. Eg. apple in english,seb in hindi is the name of same fruit in different languages. This creates problem because if we speak the common hindi name of parrot in Tamilnadu they will not understand what we are talking about. These difficilties urged biologists to name plants and animals according to binomial nomenclature.
In binomial nomenclature there is a generic name and a specific name. First letter of generic name is written in capital while specific name is wtitten in small. Generic and specific name should be seperately underlined if handwritten and italicized when typed.All the name should be in Latin.