The reason there is a limit parameter for blob/clob columns is to provide optional error checking. It allows the database/application designer to set an upper limit that is lower than the maximum storable size of 1 GB, so that an errant application doesn't store some unreasonably large lob when the value is supposed to be small.
Examples:
- When storing thumbnail images it would be wrong for the application to store a full sized image.
- Very large sizes for stored digital signatures, which are normally small, would also suggest an error.
- An application may have limits on the file sizes it can process. A limit on the size of the LOB in the Data Dictionary could be used to enforce the limit.
The value of a LOB size limit has no effect on how the data are stored nor on performance. Therefore, setting a limit much higher than the amount of data stored in the CLOB/BLOB field does not introduce any other problem.
