The LDA is unique to a job and is normally used for storing temporary settings or data. This dates back to the System/36 which didn’t allow calling of programs with parameters and didn’t have a QTEMP library.
Modern programs tend to use the QTEMP library instead.
Submitted jobs have their own LDA.
If you modify the LDA in your interactive job and then submit a batch job, the LDA in that batch job will contain the same values as the job it is submitted from. This is an easy way to pass data to a batch job. The LDA can be read in a CL program, and RPG program or a Cobol program.