Would "fat" tires help me learn skinnies/log rides? I'm relatively new to mountain biking, and am considering purchasing a new, less expensive bike to help me learn to ride wooden obstacles (skinnies, curved bridges, etc.) without fear of damaging my "good" mountain bike in a hard fall.

I've also wanted to pick up a snow bike (or "fat bike"), but can't really justify the cost considering my area gets, at most, 3 or so snowstorms per year. But looking at these two issues together makes me wonder: would the wider, lower-pressure tires on a snow bike make it easier to learn correct technique &amp; feel for riding on slick, wooden obstacles? What would be the benefits/drawbacks of very wide vs. standard-width MTB tires in this scenario?
From my experience, no they would not. Have you ever watched anyone ride a fatbike? Their front tire wobbles all over the place, the extra weight from the heavy tires makes fine-adjustments much more difficult, putting extra fatigue on your body. That being said, training with a bike that's not suited for skinnys will make riding them easier when you hop on a bike that is suited for skinnys.


                
            

Tires don't help you balance on a bike as much as frame geometry does, particularly head-tube angle. I've found that down hill bikes with a more aggressive head-tube angle are actually more difficult to balance on skinnys. You don't need a fancy bike to ride skinnys unless you're doing big drops, if you're worried about wrecking your bike while learning, then get a cheap yardsale bike that you can trash and practice with. Also, wide low-pressure tires make it easier to slip off the sides of the especially narrow skinnys, I've got scars on my face to prove it.

When I was a kid we would practice our balance in our backyards, riding on 2x4's just laying on the ground or across a couple logs, or by trying to stay on the painted lines on the roads, or riding on the curb of the sidewalk. Slow races are great for balance too. We'd race like 10 feet, and the last one across the line won. Basically, whoever was the best at brake stands had the advantage.