I'm new to 4x4 driving and need a few basic questions answering!

I've been driving my recently acquired 94 Cherokee in 2wd in dry conditions, but my gf drives her 98 Grand Cherokee in 4wd all the time. After some Googling, what I can gather is that 4wd should be used all the time for greater stability, if this is so; what is the useful application for 2wd? I'm sure I'm wrong, but doesn't the apparent benefit of 4wd make 2wd superfluous?

Also, her Jeep has a button on the dash marked "D OFF", what is this for?

(btw - neither of us has a handbook for our Jeeps!)

Thanks.

 

she may havefull time 4wd. you on the other hand proply only have part time.

 

Hers has 4wd - N - 4wd lo marked on the shift, mine has 2wd - 4wd p/t - 4wd - N - 4wd lo