Have you ever try to drop a table with size sat us say 20GB or more?? It may take several hours/days because of considerable amount of CPU processing. Most of the processing time takes place in updation of extents (used to free) in data dictionary.

You can split out this process of dropping a table to save resources. Let us assume that our table is of size 20GB.

Follow this steps:
1 TRUNCATE TABLE T1 REUSE STORAGE;
This command will not deallocate extents but resets the HWM to segment header block. Hence it won't take much time.
2 ALTER TABLE T1 DEALLOCATE UNUSED KEEP 15G;
3 ALTER TABLE T1 DEALLOCATE UNUSED KEEP 10G;
4 ALTER TABLE T1 DEALLOCATE UNUSED KEEP 5G;
5 DROP TABLE T1;

(You can split out this process over different timings/days)