what's the point of std::unique_ptr::get

Doesn't std::unique_ptr::get defeat the purpose of having a unique_ptr in the first place? I would have expected this function to change its state so it holds no more pointer. Is there an actual useful use of std::unique_ptr::get?

std::unique_ptr provides unique ownership semantics safely. However that doesn't rule out the need for non-owning pointers. std::shared_ptr has a non-owning counterpart, std::weak_ptr. Raw pointers operate as std::unique_ptr's non-owning counterpart.

You use it every time you need to pass raw pointer to, say, a C function:

std::unique_ptr<char[]> buffer( new char[1024] );
// ... fill the buffer
int rc = ::write( fd, buffer.get(), len );