DEFERRED_SEGMENT_CREATION parameter  specifies how segments will be created for the table and its objects like index.

 

DEFERRED_SEGMENT_CREATION=TRUE     —–>>segments for tables and their dependent objects (indexes) will not be created until the first row is inserted into the table.
DEFERRED_SEGMENT_CREATION=FALSE  ——->>As soon as table/index is created, segments will be created (even though no data is present) 

Setting this parameter to true will save disk space, if we expect lot of empty tables in the database.

Lets see the below example:->

When DEFERRED_SEGMENT_CREATION=TRUE( THIS IS THE DEFAULT ONE)

We can see, it haven’t created the segments. So if you expect lot of empty tables in your database, setting this parameter to TRUE, will save lot of disk space.

Now set to FALSE, do the same test:

 

We can see, as soon as we create the table and and index, the segment got created ,despite it does not   contain any data.