The TJ flares will enable more wheel trave for the rear tire, less body contact! The process of flat-fendering(FF) (if such a word exhist) offers couple of benefits.
1. If you want to extend the wheel base, this is neccesary!
2. If you like to tackle obsticals straight on (and this would only work with little to no front bumper), you have more exposed contact area for you tire to climb said obsticle.
3. If you should be in a extremely off-chaimber situation, the sheet metal would not be in the way! or if you are real close to a tree, no hitting!
4. looks F-in cool!
Now the down side of these mods.
1. when you use a TJ flare on a YJ and FF it, you loose the side markers, no biggy but they are gone.
2. In order to make it 100% functional, you will need to cut you bumper down to about 46" or less, not exactly legal in all states!
3. unless you have a front locker or a tire large enough to get over something that would have had the fender in the way before, then it is purely cosmetic!