My $.02 worth...It's a lot easier to adjust to another person for a single night than it is on a long trip. It's pretty easy to adjust to someone's quirks for a single night. But if you're sharing a month or more together on a long trip, I think you'd want to know a little more about each other's traveling style.
I've had both good and less good experiences with folks I didn't know prior to leaving on a trip. Every single one of them was a fine fellow. However, our traveling styles didn't always mesh well.