Hello, I have a question.
Following content is written in P.148 this book.

"To prevent metadata keys from appearing in the custom fields meta box on the post edit screen, prefix the meta key with an underscore like "_prowp_price. This will hide the data from the user and is common practice when creating meta boxes."

I would like to ask about preceding above contents.

1. Why meta key prevent from appearing in the Custom Fields is better?
2. Could you please show me sample codes that using this prefix?