How does autocommit=off affects bulk inserts performance in mysql using innodb?
If autocommit is turned off, you can always do a ROLLBACK to get back to the state the database was in before you started doing something.
COMMIT makes sure all changes to the database are written permanently, doing this for every INSERT takes more time than doing this for a  lot of INSERTs, because not only the records needs to be inserted, also the indexes needs to be updated. Doing this last piece for a lot of records is more efficient than doing this for 1 record at a time.