I have a Patrol w/2 wheel drive. There is a road near me with multiple water crossing in the 3-6" range. I only switch it into 2WD when there have been heavy rains and 3-6" turns into more like 6-10". I'm pretty sure I would not really need it even then but there is no way I want to find out, mid-stream. Basically unless you are doing heavy off road riding in deep stuff I doubt it would be necessary. The exception to that as Windmill points out is snow. In snow and ice it can be very, very handy which is why I bought it
My lab is 85 pounds and he has plenty of room. I've also had 6'6" guys in there who are pushing 250 so I doubt a 100lb+ dog is going to be a problem. Actually one of the not-so-obvious benefits of a Ural is the amount of stuff you can carry. A well equipped touring bike might be able to handle a few weeks worth of kit. A Ural could carry a month or two's worth to say nothing of a weeks woth of groceries, a keg of beer, firewood, tools to build a log cabin and just a out anything else you can think of. If no one is sitting in the chair there is a whole lot of space for carrying stuff and that's before you even open the trunk.