If a table or index becomes fragmented (not continuous on disk) performance can decrease. You can see which objects have over 10 extents with:
select * from dba_segments where extents > 10;
If it is more than 10 it is a candidate for rebuilding.
- Export the table (with compress=Y)
- Drop the table
- Import the table
- Use Flex2SQL to drop and recreate it. Possibly hand crafting the 'next' storage parameter
Recommendation: Inform customers to check their tables that have possible performance and if they do, recreate them.