Most 4 wheel drive systems need a little slip when turning. Pavement, or rather, turning on pavement while in 4 wheel drive, can damage the front end drive components.
That said, 4 wheel drive needs to be engaged and ran on a somewhat frequent basis as this keeps the seals and other parts properly lubricated.
If you're pulling on gravel that's a perfect time to engage it. Use it every once in awhile just to make sure everything works and to let it turn a little.
Hard surfaces with lots of grip.....no, don't use it.
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.