Really, there are no advantages if you figure the cost vs buying aftermarket wheels with the backspacing one may get with a spacer. One thing to keep in mind is by "spacer" we are really referring to what is an adapter ring mounted on the rotor or drum, that has its own studs for mounting wheels. What we are not referring to are "rings" that look like large washers with holes to mount over the existing axle studs. These rings are not recommended for street use and depending on the thickness of the ring, will reduce the effective mounting surface of the stud as it mates with the lug nut. Usually due to liability reasons, many tire shops will not touch a wheel mounted on a ring spacer.
I run personally run the adapter type spacer. Why? Well, I always liked the way my OEM Gambler wheels looked and wanted to keep them, even after I upgraded my tires from 31" up to 33x10.5 KM1s. My problem with the larger tire size, is the higher backspacing typical on OEM wheels. Gamblers have a backspacing of 5.25". With the stock backspacing and 33" tires, I noticed I rubbed on my passenger side SwayLOC arm, during full left turn locks. I definitely needed to decrease the backspacing of my wheels to mitigate the rubbing. Note: I did not rub during full right turns, so I suspect that with the 33x10.5" width, I would be ok with 5.25" BS if I had the stock antisway bar.
The 1.25" adapters I use, plus the 5.25" Gambler wheels - nets me a backspacing of 4" which definitely helps me clear my SwayLOC arms. I believe 4" is an appropriate BS for most 33x12.5 tires.
Adapters also bring additional maintenance into the picture. Because you have added another component to your Jeep, it is a another potential failure point if neglected. I always check my torque settings on my adapters every time I rotate my tires, if not more.