If you delete most of the rows in one table, you probably want to regain that space, to minimize IO and fragmentation.
If you delete most of the rows in most of the tables, you probably also want to resize the datafile to reduce storage and backup space.
In this case, you could move your data in a new tablespace
alter table t move tablespace newts;
I wrote about this here : 2006/08/tablespace-maintenance-tasks.html
There is also an option to SHRINK. In oldish (pre-12cR2) releases, this had the advantage of being an online operation. In 12.2, include the online keyword.
SHRINK requires ROW MOVEMENT. I don’t like the idea of having the rowid’s changing. You have also a bunch of restrictions, amoung others on materialized view fast refreshes and index organized tables.
I am impatient to get this 12cR2. According to the doc, during an alter table move, transactions run uninterrupted on the table