One reason common names are not useful to biologists is that they

Well, in binomial nomenclature, it's Latin so everyone can use them, wherever they are from. If an English biologist says "tiger" in their language, a Spanish biologist may not understand. However, if they say "Panthera tigris," the Spanish biologist will be able to understand because of the shared language of Latin. I hope this helped!

As you might be able to appreciate, it would be difficult for people speaking or writing in different languages to know when they are talking about the same organism. This problem was resolved by agreeing upon a ‘scientific’ name for organisms in the same manner that chemical symbols and formulae for various substances are used the world over. The scientific name for an organism is thus unique and can be used to identify it anywhere in the world. The system of scientific naming or nomenclature we use today was introduced by Carolus Linnaeus in the eighteenth century. The scientific name of an organism is the result of the process of classification which puts it along with the organisms it is most related to. But when we actually name the species, we do not list out the whole hierarchy of groups it belongs to. Instead, we limit ourselves to writing the name of the genus and species of that particular organism. The world over, it has been agreed that both these names will be used in Latin forms.
Certain conventions are followed while writing the scientific names:
1. The name of the genus begins with a capital letter.
2. The name of the species begins with a small letter.
3. When printed, the scientific name is given in italics.
4. When written by hand, the genus name and the species name have to be underlined separately. 
The binomial nomenclature makes for a uniform way of identification of the vast diversity of life around us.

All the Best. :D