It varies.
When I was playing competitive tournaments, I'd spend practice rounds checking out, as much as anything, where to NOT miss shots. Also, dependent upon weather conditions, practicing different types of shots from different yardages, from different parts of the course....fairways, rough and around the greens. Judging from my anemic record, the preparation seems to have been in vain.
When traveling somewhere to play a course or courses on a golf trip, my research normally consisted of finding a nice place to stay, as well as checking out places to eat. Usually on these golf trips, we played the same course multiple times, so experience and charm was gained with each round. My preparation was hit a few balls and putts, stretch and some caffeine intake. That's about it.
Of course, with the advent and advancement of the Internet, pretty much anything is now available at our fingertips, but a great deal of that information is second or third hand opinions. Sure pictures and Google Earth are great tools, but for me, it can serve up a healthy dose of expectation, which I now try to avoid as much as possible.
I guess it's like having a first date with a beautiful, charming, intelligent person. Why look at their social media presence or what somebody's cousin's co-worker has to say about said person? I'd rather go to dinner and enjoy their company, maybe a 2nd dinner and form an opinion of my own afterwards?