If you spend more time onroad then they can help. You should have less wander. The ride may become smoother as the leaf isn't fighting the shackle.
The downsides is that you'll get more dive when braking hard. If you're steering isn't set up right you'll get more bumpsteer. The other problem is with the front driveshaft. If the driveshaft is too long you'll end up punching the transfer case.
There are some other things to be aware of. Some shackle kits add lift, others don't. Don't go with a bolt-on. Not only does it add lift it will reduce your approach angle.
Although if you have other problems, it probably won't fix it.