Your academic advisor is responsible for observing, discussing student progress and offering helpful recommendations for improvement. Oftentimes an advisor can be the person that observes a student's progress and development over the course of their studies, and is best equipped to discuss academic issues on an individual basis.
An advisor is also responsible for making sure that students are meeting the academic requirements of the program. In the event that a student is not producing at the level of others, the advisor should meet with the student and discuss the problem, and make recommendations for the student to follow concerning their studies.
Academic advisors sometimes also double as faculty members, in which case they may be difficult to track down. It is important for all students to make the effort to meet with their advisor. If a program offers a combination of required core classes, electives and other options, it is the advisor that can help a student determine whether they are meeting the requirements of their program.