What are the benefits of SQL in a C++ application instead of a class object containing binary file?

I'm making a C++ and QML application with Qt. It's basically about collecting, manipulating, and querying the data of individuals with a fancy UI. Qt has it's own SQL implementation, but I don't see the reason to use it for my needs over a simple binary file with class instances containing all the data I need to store. I can easily create functions to manipulate this data from the file and encrypt it after each use for security. Using SQL, I think, would only require me to learn all of the commands and the Qt SQL implementation. Still, I'm ready to do it if there are any real advantages. Any wise words? Thank you!