I'm on the fence about this but haven't carried through with it yet. But to answer why (for me), it would prevent the ng from being so unruly. I would spritz it with a little water so that it can wave back up slightly so that the ng can be seen.Detangling my hair, yes.
But straightening it.....not seeing the logic there I guess.
No I don't straighten, but my stylist can be lethal on my NG when she is trying to part the hair.
The next time I touch up I'm going to wash and rollerset my hair 24 hours before I relax. This way my NG, in theory should be more manageable.