I'd tell them to definitely participate in the short-term summer program for various reasons:
1. It helps you learn about an interesting subject which you probably haven't thought about before or even learn more about the matters you already know and discuss it with people who are experienced in your field of interest.
2. It's a great opportunity to learn more about the EPS department and opportunities available which will be extremely useful especially if you're considering to choose a concentration related to the EPS department.
3. Even if you're interested in other fields, participating in the short-term summer programs helps you learn about something related to another field and in cases which no background is required, you'll definitely enjoy learning about new matters.