Regarding the front axle being engaged all the time:
Jeep got rid of the locking hubs a long time ago, and now the front axle is "live" all the time, with the front driveshaft spinning at all times, whether the transfer case is selected for 2WD or 4WD. When you shift the transfer case into 4WD, it simply locks the front driveshaft to the rear. Result: instant 4WD! No waiting around for a central axle disconnect to engage....
That's one thing I really like about my Jeep (1997 Wrangler TJ): as soon as I pull the lever up on the transfer case, I'm in 4WD ready to blaze trails. If I want to go back to 2WD, just push the lever back down. No waiting time needed.
By having the front driveshaft spinning at all times, it allows you to shift into 4WD on the fly as well.
Casey
1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter