Language acquisition improvement?
I had a home stay so I was able to practice with the woman my roommate and I lived with. Other home stays were family sized, mine was just one old, single woman, not uncommon apparently. I was also able to practice in the classrooms and with some of the more dedicated students. The downside is that Barcelona is an international hub where the locals speak Catalayn (mixture of Spanish and French), a language only spoken in this part of the world. So, all the locals also speak Spanish, or learn English, French, Arabic, German, Italian, etc. For most students they got by with speaking in English all the time.
So If your looking to just experience Europe and don't care about learning Spanish, the you won't have any difficulties at all.
On the other hand, if you want to improve your spanish, outside of the university you may find it more difficult. Most students in the programs will just talk in English, when you go to a shop the owners are either annoyed to talk to you out of their native Catalayn or extremely excited to practice their English with you. Only a few times was I able to disguise my american accent when speaking spanish, but even then they know your not from Barcelona because your not speaking Catalayn and they treat you like a tourist.