Many developers go down the path of writing their raw data in the schemaless format like JSON. This is appealing because of how easy is is to get started, but this approach quickly leads to problems. Whether due to bugs or misunderstandings between different developers, data corruption inevitably occurs. (#)
At 9:50 schema is very very important. (#)
At 11:55 you need to enforce schemas at produce time (#)
When you create an enforceable schema, you get errors at the time of writing the data -- giving you full context as to how and why the data became invalid (like a stacktrace). In addition, the error prevents the program from corrupting the master dataset by writing that data. (#)