One good point is that if you keep all the data for a specific week or set of weeks in separate tablespace, you can in some point in time make the TS read only, when data will not change anymore and hence make the backup easyer and faster ( since you backup the read only tablespaces only once)
Later you could put the TS on read only media, and even plug it out of the database and plug it back in when needed ( that's possible since 9i and there is special feature for that in 10g)
So to summarize, this will allow you to know where physically the data for specific period resides and hence drop/move/archive/backup easyer
Of cource that maight be not relevant at all in your case