Regardless of what you do or where you are in the world this money will always be paid to you. This is the advantage of passive income. Once it is set up the money comes rolling in regardless of your personal circumstances.
It may not be a great deal, but every little helps. Once you start thinking about retirement then every bit of extra income is a blessing.
Interest on money is one simple instance of passive income but there are many others.
Some years ago I wrote a technical book which was published by a world renowned publisher. It was a steep learning curve initially, but I have since been invited to write other books by the same publisher.
This has led to a small library of books (translated into several languages) on which I now receive a passive income stream in the form of royalties. I can still do a day job as once the books are published they need no further input from me. All I do is to bank the royalty payments every quarter.
Writing a book is not that difficult to do. Many people have specialist knowledge that they use every day in their job or at home or in a specialist hobby and writing is just a means of sharing this knowledge with other people. You may think that your knowledge is insignificant but there are always a number of people who are glad to share your knowledge.