Pro's and Cons of "narrow" and "wide" tires

I've been poking around google trying to the the pro's and cons of both "wide" and "narrow" tires. That being said what would be a narrow off road tire? 10.5? 11.5, 12.5? and where would a wide tire start? I've seen a few different augments be it on jeep sites, toyota sites and so on. So given the weight of our trucks what would be I guess an "ideal" size and what would the pro's and cons be of each?

So far one simple thing I got is MPG's narrow tire = less friction= better fuel mileage but whats the down side?

I'm intrested to see what everyone comes up with on this, I would say my tires depend on this but I just ordered mine....hope I like them