They are optional. They help prevent problems when people don't take their time tightening down the lug nuts in a proper sequence, and proper torque. In some applications they can prevent the wheel from touching the calipers and such as you slide the wheel on. However you don't need them.
Take your time, hold the wheel centered best you can, and tighten the wheel down in stages, don't just jump straight to 80 ft-lbs, it won't be a problem.
Lots of other posts on this too if you search on this if you rdon't want to take just my word on it,
take this one for example