Why doesn't the Compose state only update UI component but also relaunch logic code in Android Studio?

Before Compose, I use LiveData to connect between UI component and data, the UI component will be updated when the data of LiveData type has changed. After I use Compose, I was told that MutableState<T> is just like LiveData, but it is used in Compose.

In the following Code A, val count is MutableState<T> type in Part 1, so the text will be changed in Part 2 when I click the button in Part 3. The above procedure is easy to understand, just like I use LiveData before.

But "3 times clicked" will be displayed when I click the button for 3 times, I don’t understand why Part 4 is launched, you know if (count.value == 3)... is a logic code and it’s not associated with any UI component.

1: Does it mean that the system will observe all code which are associated with val count, and run it automatically when the count.value is changed?

2: Will Part 5 always be relaunched when I click the button in Part 3 ?

Code A

@Composable
fun Counter() {

    Column {
        //Part 1
        val count = remember { mutableStateOf(0) }

       //Part 2
        Text(
            text = "I've been clicked ${count.value} times",
        )

        //Part 3
        Button(onClick = { count.value++ }) {
            Text("Click me")
        }
       
        //Part 4       
        if (count.value == 3) {
            Log.e("My","This is test")
            Toast.makeText(LocalContext.current, "3 times clicked", Toast.LENGTH_LONG).show()
        }

        //Part 5
        Log.e("My","Is it always displayed?")
        Toast.makeText(LocalContext.current, "Is it always displayed", Toast.LENGTH_LONG).show()
    }
}



class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            BasicsCodelabTheme {
                Surface{
                    Counter()
                }
            }
        }
    }
}

Added Content

In Code B, I know the Part A will be relaunched when the value of displayFullItemByID has changed.

1. Will Part B be relaunched when the value of displayFullItemByID has changed ?

2. Will Part C be relaunched when the value of displayFullItemByID has changed and it’s equal to 5 ?

Code B

class VoiceAdapters (private val aHomeViewModel: HomeViewModel) {

     fun bind(inputMVoice: MVoice) {                        
           aHomeViewModel.displayFullItemByID.observe(mLifecycleOwner) {
                //Part A
                _isDisplayed.value = inputMVoice.id == it
            }
 
               //Part B
            Log.e("My","Can I relaunched in Part B")
            
            if (aHomeViewModel.displayFullItemByID.value==5) {
                //Part C
                Log.e("My","Can I relaunched in Part C") 
            }
    }

}

class HomeViewModel() : AndroidViewModel(mApplication) {
    private val _displayFullItemByID = MutableLiveData(-1)
    val displayFullItemByID: LiveData<Int> = _displayFullItemByID
    ...
}