Variable length reduces the amount of data that the Data Integration Service stores in the sorter cache and the disk space consumption on the Data Integration Service machine.

For example, you store data on customers. Some customers have longer names than other customers. If the Data Integration Service uses fixed length to store the data on customer names, the Data Integration Service might store data on 20 characters for each name. If the Data Integration Service uses variable length, the Data Integration Service might store data with an average length of 10 characters.