The direct answer to this is YES, you absolutely need them if your vehicle is currently utilizing strut as a factory suspension component.  If you absolutely do not want a strut assembly and are willing to do a lot of fabrication work then installing a bag is also a possibility as long as your not substituting a McPherson strut.  You will know if your front struts are McPherson by simply verifying whether you have an upper control arm or don’t.

McPherson struts allow the spindle and strut to move simultaneously and has the ability to spin with the steering. This allows all the entire vehicle suspension structure to rest on the strut and lower control arm.  Alignment is then achieved through your strut adjustments or the lower control arm.  In this case no upper control arms are necessary. A general picture of this is represented below:

The alternative top this type of suspension which is seen in larger vehicles and trucks is the double wishbone style suspension. This is easily distinguished by the upper and lower control arms.

These double wishbone suspension configurations are generally stronger.