What is the use and importance of recommendation letters?
In some other places, such as the US, no one would likely view them as nepotism unless they came from a relative. 

The purpose is to give the receiving institution an independent evaluation of the candidate from someone, such as a professor, who is in a position to know both the background and the likelihood of success of that person. Usually the recommender has some standing in the academic or professional community and who can be trusted to give an honest evaluation. 

In many places, such as the US, they are all important, outweighing many other factors. It is unlikely you would be admitted to a program based only on letters, but very difficult without good and supporting letters. Don't neglect them if you are applying internationally.