What are the advantages

 

Where do you ride? One thing i was taught back in the olden days, The mailman has it right, meaning that they always ran those tall thin tires on the mail jeeps. They cut a track on any road surface, dirt, rock, mud, snow, slush, rain. The military used them for years on almost all surfaces. Another way to look at it though is deep mud, soft ground, or sand. Wide fat tires work better, although those thin ones can be aired down for soft loose surfaces (read sand) to about 12-15 lbs and you'll be in like Flynn. Whatever you choose is usually personal preference. I still run a 235/75/15 and have never had a problem. Normal pressure on road, snow, rain, etc.; and aired down for sand when im out fishing at the coast. Wide tires are cool though, and you can do some great ice skating with em.

 

Skinnier tires will allow you to run a closer to stock back spacing rims, with out rubbing.

 

Thinking of running 235 85 16 because they are a heavyer ply and for further upgrade down the road 16s just seem more availble

 

Skinnier are lighter and have a smaller contact area so technically better for mpg's. Big debat that they are better in the mud because they cut through it instead of float. Easier to fit in the fender wells also.

 

skinny tires are better for snow they say, and wide for mud

 

A skinny tire has a smaller contact patch which equals less rolling resistance and increased mileage. They are also lighter so less effort is required to start them rolling and to stop them.
Wider tires provide a larger contact patch which translates to improved grip on dry road surfaces but increased hydroplane risk in wet conditions.
As far as off road I don't see any advantage of a narrow over a wide tire unless you are in competitive mudding. If you look at these guys, all run tall skinny tractor tires to cut through the mud as opposed to go over it. The larger contact patch will give you better traction all around and a higher "flotation" ability on soft terrain.

 

It's also easier to steer a skinnier tire than a wider tire