UNWIND-PROTECT is a building block.

Resource management in the MIT Lisp OS ca. 1980, approximate example.

One would define a resource of arrays, where arrays can be allocated and deallocated. They will be managed via a pool.

    (defresource 2d-array (rows columns)
      :constructor (make-array (list rows columns)))

Now user code would use the USING-RESOURCE macro, where it spans a dynamic scope. Entering the scope allocates the resource. Inside the scope the resource is allocated. Leaving the scope will automatically deallocate the resource and put it back into the pool. A deinitializer may free memory as needed.

    (using-resource (my-array 2d-array 100 100) ; get me a 100x100 array from a pool
      (setf (aref my-array 42 42) 'the-answer)  ; setting the array
      (print (aref my-array 42 42)))            ; reading the array

To make sure that the resource gets deallocated, the above macro form will expand to something using UNWIND-PROTECT:

    ...
     (unwind-protect                                            

       (progn                                                   ; protected form
         (setf my-array (allocate-resource '2d-array 100 100))  ;   allocate the array
         (setf (aref my-array 42 42) 'the-answer)               ;   setting the array
         (print (aref my-array 42 42)))                         ;  reading the array

       (when my-array                                           ; exit form
         (deallocate-resource '2d-array my-array)))             ;   deallocate the array
    ...

This is an example of manual memory management using a pool of resources, where the DEALLOCATE is done always via UNWIND-PROTECT.

Thus the user will not explicitly use UNWIND-PROTECT, but some macros which use it in their expansion...