My rig is just over 29' feet long, 8.5' wide, 13' tall, weighs over 11 tons fully loaded. There's plenty of places I can't squeeze into traveling in North America, let alone other parts of the world. I end up doing a lot of scouting on a dirt bike before venturing down an unknown, unmarked route. You end up thinking a lot about where you'll be able to turn around! And the recovery scenarios for a rig of this size are much more technical and demanding. Even though I'm rigged and trained for recovery ($$$$) I'm very conservative about where I go because I just don't want to get stuck, or risk serious damage to a very expensive camper box. And while changing a tire isn't quite as scary, it's a serious and time consuming job (each weighs over 250lbs).
So for me, size and weight not only limit where I can fit or what I can drive over, but also reduce my willingness to expose my rig and occupants to risk. I love motorcycle travel anywhere, but it's definitely been my preference outside the US because it opens up so much available terrain- but you sacrifice a lot of comfort. This site is full of compact overland campers that are a great mix of comfort and capability. Anything much wider than 2M or 90", taller than 3M or 108", and longer than 7M or 23', and heavier than 5 tons puts you into a significantly more demanding vehicle management scenario, IMHO. Then again, it is kinda fun to drive a mongo rig around!