This you can use to isolate transactions within the session, and commit at the end. For an example, if you want to load data from various sources into a table, you can set the Transaction for each procedure step to the same transaction isolation value, with the 'Commit' as 'No commit' and when all data is loaded into the table, have a commit step in your procedure to commit that specific transaction. If for some reason a step fails, then no data within that transaction will be committed to the database.
Its the same as using SQL Developer and having auto commit turned off. You have to manually commit to the database if you want to see the data changes in another session, or you can Role Back your changes within the session if you do not want to commit them.
Have a look at the IKM 'IKM Oracle Incremental Update' - this uses Transaction 1 on the following steps, both have a specified 'No Commit':
'update existing rows'
'Insert new rows',
then has a specific commit step afterwards.