What are “rvalue references for *this” for?

Question

What are the most typical use cases of \"rvalue references for *this\" which the standard also calls reference qualifiers for member functions?

By the way, there is

Answer 1

Some operations can be more efficient when called on rvalues so overloading on the value category of *this allows the most efficient implementation to be used automatically e.g.

struct Buffer
{
  std::string m_data;
public:
  std::string str() const& { return m_data; }        // copies data
  std::string str()&& { return std::move(m_data); }  // moves data
};

(This optimisation could be done for std::ostringstream, but hasn't been formally proposed AFAIK.)

Some operations don't make sense to call on rvalues, so overloading on *this allows the rvalue form to be deleted:

struct Foo
{
  void mutate()&;
  void mutate()&& = delete;
};

I haven't actually needed to use this feature yet, but maybe I'll find more uses for it now that the two compilers I care about support it.