A variable-length record with variable-length subfields is a very efficient way to store variable length data.
The second way to establish a database is via variable-length records where the length of each field is indeterminate.
For serial devices, including tape, variable-length records make a lot of sense.
The variable-length record is the basis of a MARC record.
Revelation, by Cosmos, is one exception to this rule, because it uses variable-length records.