Spending a term abroad or submatriculate?

My son is a sophomore doing computer science in Penn. He is also pursuing a dual degree in the College majoring in Economics. Whilst he is considering to spend a term overseas like the University College London or ETH Zurich, he can have the opportunity of topping up the credits for submatriculating. He needs additional seven credits to get a master in CIS. Can anybody encounter such choice in Penn and what are the beauties of studying abroad and the option of submatriculating, especially in terms of career development?