Most people don't really need manual hubs. Their conversion kits are expensive to buy, they require upkeep, and they don't (as some ads say) improve mpg or power enough to be able to calculate or notice.
My stolen TJ and my present TJ have manual hubs but they are really primarily to be able to disengage the axles in case something breaks, axle shaft or ring & pinion gear, so the axle can still be driven on.
They are handy if you have a front automatic locker for when you want to be in 4Lo but you don't want the front locker engaged. Unlocking the front hubs then give you a "2Lo" mode which I ran a lot of trails in. 2Lo gives you the benefit of 4Lo's low trail speed without the increased steering effort a front locker gives on some trails.
For the >$1000 it usually costs to convert to manual hubs up front, they aren't really worth it for most offroaders. You certainly don't want to want them for better mpg or power because neither of those will happen.