why do we pass a pointer to vector in function code example

Example: how to make struct type as array in go

package main
 
import "fmt"
 
type rectangle struct {
	length  int
	breadth int
	color   string
}
 
func main() {
	rect1 := new(rectangle) // rect1 is a pointer to an instance of rectangle
	rect1.length = 10
	rect1.breadth = 20
	rect1.color = "Green"
	fmt.Println(rect1)
 
	var rect2 = new(rectangle) // rect2 is an instance of rectangle
	rect2.length = 10
	rect2.color = "Red"
	fmt.Println(rect2)
}