before submit: operate on the "live" record, validate, modify. The new data (or new record) hasn't yet impacted the database. After submit: your record is saved, you have its id. Modifying it is more complex, and will be more performance taxing because it will require another db operation. But as you now have the id, you might want to do some related tasks with that record... attach it to some other record... send an email with its data... etc etc.