I don't want to have to deal with locks if at all possible. Binary works fine if each file is atomic, but that does not sound like the case you are advocating.
And in most applications you don't ever have to deal with locks as most applications don't need multiple threads writing and reading, that can be done with a single thread and a lockless queue that multiple threads write to. You would need a lock for making backups of the files themselves but this is trivial and takes the form of error handling. The OS itself handles the lock, you just need to handle the case where you can't open the file for writing.
This approach is not all that rare, lightweight, and very useful for minimizing latency. Why would you ever use a database if you don't actually need the features? It is much simpler to immediately have access to all your data in your application's data models.