why name publicizing is there when we want to inherit the base class privately?

Generally, we wish to use private inheritance to hide the implementation details to the base class. If this is true,

1) Why is the name publicizing feature is there again ? Is it only for language completeness or is there any practical usage also?

2) Even though I publicize the base class function name, a derived class can still declare another function with same name. Please consider the following code.

#include "iostream"
using namespace std;

class Base {
  public:
    int zoo;
    Base() {zoo =5;}
    int sleep() const {return 3;}
};

class Derived : Base { // Private inheritance
  public:
    using Base::zoo;
    using Base::sleep;
    int sleep() const { return 4.0; }
};

int main() {
    Derived der;
    der.sleep();
    cout<<" zoo is : "<<der.zoo<<endl;
    cout<<" Sleep is : "<<der.sleep()<<endl;
 }

In the above snippet, even though we publicize the name, we can still declare the name in derived class, and we can access the base class version of member variables. How the memory is managed?

Thank you.

http://en.cppreference.com/w/cpp/language/using_declaration

If the derived class already has a member with the same name, parameter list, and qualifications, the derived class member hides or overrides (doesn't conflict with) the member that is introduced from the base class.

That link has specific examples of exactly what you are doing an re-iterates what I quoted above and how the base member is simply hidden by the derived member.