Reminder. Max size of Datafile is concerned with the 32-bit/64-bit OS. You can't move around your instance across boxes if you get the situation of creating TEST/DEVT instances for Production.

Once, you 64-bit, you have to keep going with 64-bit. This does matter alot if your database grows more than 50//100GB. For smmaler size, it will not make much diffrence, as you can always export and import.