The scope of what you do on a surgery sub-i depends on a variety of factors: what program you go to, how many other students are rotating at the time, how many hospitals you rotate through, etc. Simply put, the role of the sub-i is to perform all the clinical duties of an intern, i.e. Acting Internship and therefore demonstrate the competency and skill required to become a successful resident. How well you accomplish that task is entirely in your control. If you are interested in seeing exactly what you will be asked to do on a specific sub-i, simply google the program & the course description.