In the original feature, the TSL_Put() UDR was overloaded to take either an lvarchar argument or a CLOB argument to specify the elements to load. In many cases, the client programs would use the lvarchar version of TSL_Put() UDR to load element by reading reading a file and creating one or more lvarchar values and then call TSL_Put successively. This adds complexity to the client.
With the CLOB argument, we found most users had a file and used the SQL function FILETOCLOB to create a CLOB value then called TSL_Put UDR with the clob to load the elements. This caused the file to be read and then written to a CLOB, then TSL_Put would read the clob. This resulted in the data being read twice, once from the file and once from the CLOB.
Starting in Informix 12.10.xC5, if you have a file of element values that is accessible to the Informix Server, you can use a third version of TSL_Put:
execute function TSL_Put(handle, 'file:/path/filename');
The TSL_Put() UDR will read the element values in the file directly. This can make the clients easier to implement and can reduce IO for very large element lists.