why use std::move if function already have a rvalue reference

I was reading a book about data structure implemented in c++, I dont understand a code snippet， it's part of vector class

void push_back(object &&x) {
        //do something
        objects[size++] = std::move(x);
    }

I know that std::move return a rvalue reference of the object, but the push_back member function already has rvalue reference x as parameter, isn't the std::move here unnecessary？

another question is if we have a rvalue reference of a class object, we still need to use std::move on its member if we want to call move instead of copy right? like the code below:

A& operator=(A&& other) {
     member = std::move(other.member);
     return *this;
}