Instead of a database I just serialize my data to JSON, saving and loading it to disk when necessary. All the data management is made on the program itself, which is faster AND easier than using SQL queries. For that reason I have never understood why databases are necessary at all.

Why should one use a database instead of just saving the data to disk?


You can query data in a database (ask it questions).
You can look up data from a database relatively rapidly.
You can relate data from two different tables together using JOINs.
You can create meaningful reports from data in a database.
Your data has a built-in structure to it.
Information of a given type is always stored only once.
Databases are ACID.
Databases are fault-tolerant.
Databases can handle very large data sets.
Databases are concurrent; multiple users can use them at the same time without corrupting the data.
Databases scale well. 


In short, you benefit from a wide range of well-known, proven technologies developed over many years by a wide variety of very smart people.

If you're worried that a database is overkill, check out SQLite.
