the benefit of a divorced t-case is using it behind a 2wd tranny but you have another driveshaft and joints to deal with. and you need a lot of room to make it fit.

the dual t-case is good for super low gearing. you lop off the front output of the 1st t-case and just use the hi and low.(range box) say you have 2:1 low in one and 2.5:1 in the other. this gives you several different gearing options. you can use 1:1 in both and have your regular 4 hi. you can put either one in low and have 2:1 or 2.5:1 low range. or put them both in low at the same time and have 5:1 low range. most aftermarket t-case gears are only 4:1 at best and you don't have the 2 or 2.5 to 1 option. it's either 1:1 or 4:1.

the dual t-case was best for me because i like to rock crawl where low gearing is necessary but i also go to the dunes with the same jeep. i don't have enough engine to run 1:1 in the dunes but 4 or 5 to 1 is too low for the dunes. with my dual setup (np231/d300) i can have a final low range of 7.12:1 final low or 2.62/2.72 low range when i want to go a little faster.