This appears to be a simple information gathering question, but many times it’s followed up with “What special skills or knowledge did you need to perform those duties?” These two questions combine to give the interviewer a larger view of your functional background as well as an insight into your depth of understanding. If you’ve had any specialized training, this is a perfect time to mention it. It tells your interviewer that your previous employer felt you were a good investment of the time and money spent on training (this is an endorsement in and of itself). It also tells the interviewer that such an investment won’t have to be made on his dime!