Jetpack compose bottom navigation

Question

The official example to create bottom navigation shows the need of sealed class, list of screen and such(link to official example). Why not just toggle between screen

 BottomNavigationItem(icon = {
        Icon(imageVector = Icons.Default.Person,"")
    },
        label = { Text(text = "Profile") }, 
        selected = (selectedIndex.value == 2), 
        onClick = {
            selected=Composable fun1
   }