Why do precepts practice? I can find three reasons for myself.
First, in a conventional sense, following moral guidelines makes it easier for ourselves and others. It creates a more humane and civilized society, reducing suffering and freeing up energy for more than just survival. At an individual level, it keeps us out of trouble in the world and with ourselves.
Then, it mimics what happens when what we are awakens to itself, and functions through a relatively healthy and mature human self. This helps reorganize our human self, and also prepare the ground for that shift.
Finally, it helps us notice when we are not aligned with the precepts, and inquire into why. It helps us see where we attach to stories as true and some of the dynamics around it. What do I hope to get out of clinging to this story? What actually happens? Who would I be without it? Is there validity in its reversals?