Some would argue that if a vehicle came with sway bars, then sway bars it should have. These suspension components are vital to maintaining stability and preventing body roll, which can ruin handling and present a significant danger to the driver and general public. Deleted front sway bars can make for an under-steering mess of a car, and neglecting the rear bar can result in a tail-swapping nightmare that can't be driven through a puddle without spinning out.

On the Other: You Don't Need Either

The fact is that sway bars are more of a supplemental system than anything else. Ideally, a well tuned car wouldn't need them at all, since all suspension movement would be controlled by the main springs alone. This is certainly true for the highest level drag racers like John Force and Tony Pedregon; their funny cars don't have sway bars, and they seem to manage just fine at more than 300 mph.

Bottom Line

Funny cars don't use sway bars because they go through extensive testing and suspension tuning to ensure that their spring rates are perfect. So, unless you want to spend the next six months and hundreds of thousands of dollars in tuning, then consider some sort of front and rear sway bar a necessity.

Source:

Swedish Bricks: Sway Bar FAQ

North American Subaru Impreza Owners Club: Official Sway Bar FAQ

Legacy Central: Sway Bar FAQ

More Information:

A Good Case for Sway Bars (Video)