Data is one of your most important assets in your application. Actually, it should be the fundamental asset. You might run your application anywhere, but without your data, it is pointless. By data, I mean the information that your application manipulates, generated or not by your end users. If your application can't work without a database, that database has an important piece of data that you must preserve.

Application data is very important. In web applications, users access it using the Internet and their data is stored on the server side, this importance increases. As your user base grows and the total size of your data increases, it becomes even more important to plan how your data is stored and how it's used.

And don't forget to have a backup plan. You wouldn't want to lose your data and have no way to roll back, even if the rollback means going one week back in time. Your users might accept losing some data (1 week), but will definitely not accept losing everything...