Miscellaneous Column Sizing Considerations and Guidelines
Adding a column expands the capacity required for every row in a table if the column
is not value compressible.
Dropping a column reduces every row in a table when there was uncompressed data in
the dropped column.
Specify VARCHAR for any character column for which the space savings offsets the two
bytes per row overhead and if compression on a fixed length CHARACTER column would
save less than 5% additional capacity.