Because you want to maintain an open airway while minimizing movement for suspected headneckspinal injury?

Hi, Depending on if you have received level of first aid training this will depend.

If you have basic or no training your aim is to keep the patient alive regardless of any suspected or obvious spinal injury. Therefore you should move the neck to keep the airway open and clear.

However, if you have received first aid training in the 'jaw thrust', which is where you are showing how how to open the airway with minimal damage caused to the spine.