Why was this not answered? O_e
Basically, Nature's Grasp is another way to run away and reset the fight in our advantage or get some distance for a heal. Druids are all about mobility and NG is yet another aspect of that. Root, run, heal. Root, run, nuke. Root, run, stealth. Root, /moon, run to the nearest neutral outpost.
All in all, if you can afford 1-2 points, Nature's Grasp will help you in many situations if you remember to use it. I don't know what your build is, or what you want it to be, but I wouldn't suggest trading it if it's just for a bit more DPS or something.
If the choice is between Omen of Clarity and Nature's Grasp, sure, OoC might be the better choice. But a point in Primal Tenacity and Nature's Grasp... NG wins hands down.