Hello Z,
Invisalign aligners move teeth into position by gently applying pressure on the teeth. For movement to occur accurately and fully, it is essential that the aligners fit over the teeth well. Chewies are used to help seat the aligner onto your teeth fully.
Did you ask your dentist about whether you need to use chewies? If you have doubts about your treatment it is best to ask your dentist directly. Good patient - doctor communication is one of the keys of successful treatment.