I don't have intel on SJU, but I can attest it's a valid question. As a frequent business traveler, I've been stuck overnight in a few airports. Generally fine, yet uncomfortable. But earlier this year, I was stuck in Dallas Love and thought I would ride it out (along with about 100 people throughout the airport). At about 2am, security came through to round up everyone, including the sleeping kids, to move them outside of security. Which was basically a few chairs and hard floor. Had to wait until 6am when security opened. In short, they didn't want to employ someone for those four hours at the security exit post, so they kicked everyone out and closed it tight. Pretty ridiculous. I learned at that time to not assume that I could just crash in a chair at the airport.