In the context of SQL server agent, what is a job server?

Question

When you script a SQL agent job, there will be a sp_add_jobserver invocation in the script. I checked the documentation about this stored procedure but still can't understand what is a job server. As I understand, when you create a job, you are always create it on a specific server. Later you can run the job on that server. So why we need to use this stored procedure to combine a job to a server?

Answer 1

To explan more details in here: To add a job to a different server,you must make a server the master server,and add target server(s) to it.After doing this,the SQL Server Agent in SSMS will become this:

The DelPDFHis job is target on another server:

And the target server will download it to local.

When executing the job in server a,it will execute in server b too.