Cross-country and camping always go hand in hand, and as any motorist who has spent a lot of nights in the wilderness knows, most camping times aren't as good as they look in the pictures, not to mention the weather, environment, mosquitoes, and other factors that can get in the way at any given moment.
Roof tents are a more experience-oriented option than traditional ground tents, and the advantages are obvious: easier setup, absolute flatness, and freedom from reptile infestations.
There are drawbacks, too, such as increased body height, extra wind noise, fuel consumption and, if the route involves extreme terrain, a higher center of gravity. But this has not stopped everyone from looking forward to the roof tent.