The %.* example is so close to hitting its single most useful application:

  char *something;  /* no null termination */
  size_t something_length;

  printf("%.*s", (int)something_length, something);

Unfortunately, the .* argument has type (int), not size_t, and it's signed… but if that's not a problem this is a great way to format non-\0-terminated strings.

(And of course you can also use it to print a substring without copying it around first.)