Restore is used to... well restore the contents back to the original object that was archived. ie if you had archived mydb.table1 in TD system TDDB, then you can RESTORE the that table contents from the archive to mydb.table1 in TD system TDDB. if you wanted to put in another TD system say TDDB2 you would have to use copy. or if you wanted to put it in another db/table name in the same TD System (TDDB) you would still have to use copy.
Restore ensures that all the object ids (tableid/dbid etc) match exactly as it was when it was archived. with copy, new structures and object ids are created.
There's one scenario when you can use restore to restore an Object in another TD system. That's when you first restore the DBC.