MediatorLiveData与LiveData

Question

I am not able to get the idea of MediatorLiveData while working with LiveData. In documentation it is mentioned that MediatorLiveData is a subclass of LiveData that will observe LiveData and react on onChanged method. My question is what's it's difference from having a function in observe of LiveData and do something with data if the new data is different?

For example, let's say I have query from Room Database that returns LiveData as below

@Query(“SELECT * FROM Users WHERE userid = :id”)
fun getUserById(id: String): LiveData<User>

If I want to use MediatorLiveData , I can have an extension as below

fun <T> LiveData<T>.distinctUntilChanged(): LiveData<T>{
    var lastValue: Any? = Any()
    return MediatorLiveData<T>().apply {
        addSource(this@distinctUntilChanged){
            if (it != lastValue){
                lastValue = it
                postValue(it)
            }
        }
    }
}

And then use it in my Activity as

userDao.getUserById("someId").distinctUntilChanged()
    .observe(this, user -> {/*Do something with user*/})

Contrary to above scenario, I can just have a wrapper function inside observe method as below

var lastUser = null
userDao.getUserById("someId")
    .observe(this, user -> {
        if (lastUser != user){
            lastUser = user
            /*Do something with user*/
        }
    })

Can anyone elaborate why I should use MediatorLiveData instead of just having simple check?