If properly set up, it really shouldn't be needed in most situations.
- Make sure the truck is capable and not overloaded (payload almost always runs out before tow rating)
- Make sure you have 12-15% of the trailer weight on the hitch (more if your truck can accommodate is good).
- Dial in the weight distributing hitch to get most of the weight back on the front axle.
If you do this, the sway bar is likely to be unneeded in most driving conditions. It won't hurt to use but it won't be critical.
If you have a poor setup, 3-4 sway bars may not keep it under control.