"If you are responsible for generating parquet from another format—say you are using PyArrow and Pandas for some large-scale migration—be conscious that simply creating a single parquet file gives up a major benefit of the format."

I don't understand this part, it's not clear which major benefit you're giving up, or what you should do instead. Is it saying not to convert these formats to parquet? Or that you should create multiple parquet files to get the full benefits?