Transactions in Task Flows
When you issue a commit within a bounded task flow, the entire task flow is committed as a unit. If changes have been made on multiple pages within the task flow, they are all committed.
If you have multiple pages that are based on different application modules, allowing the application modules to control the transactions means that the changes on each page get committed separately. A commit failure on one of the application modules does not prevent the other changes from being committed, because the Transaction object of each application module is separate from the others.