I was raeding this paper about space management suggested by somene here a few weeks back and I find this contradictory
Set a growth schedule for each segment in your database, and choose storage pa-rameters
that will cause Oracle Server to allocate extents on that schedule.
For any segment that grows continuously, you should choose storage parameters that moti-vate
Oracle Server to allocate a new extent to that segment about once every three to six
Then it says
Oracle Server administrators still debate whether or not allowing a segment to have more
than one extent—“extent fragmentation”—is a harmful thing.
In the first place it says we should schedule for segment to grows every 3 to 6 months that means we have to use huge extent sizes.
In the second place it basically is saying dont care about number of extents therefore size of extents. Now ths is getting me confused...
When you are about to set the extent size, you should have some possible ide about the growth rate. The reason that we all care about the extents is because that it leads to the fragmentation and later would degrade the performace. To have a better performance, you could set your tablespaces to be that of locally managed and them provide them an even auto extents. The problem of setting them on to auto extend was that you will not be aware of the rate of extents the tablespace had gone through. On the other hand this feature saves you form allways keeping a piggy back track on the tablespace from being running out of space. Any way, there would be a saturation point where one would have to do an export and import to reduce fragmentation. As a DBA you should be having a saturation point beyond which you would want to consider a defragmentaion.
I think that I have gone over board and hope this would help you to make some sense of your paper :)
Have larger extent sizes is simply to avoid recursive SQL calls which impacts database perfomance, if your extent size is small you will get tons of recursive SQL calls to update your data dictionary.
And no, tablespace fragmentation does not exist (yes Jmodic conviced me :D)