For certain inputs, compression doesn't necessarily work out so well, because of the overhead introduced by the compression format itself. For example, "compres

For certain inputs, compression doesn't necessarily work out so well, because of the overhead introduced by the compression format itself. For example, "compressing" a small datagram may actually make it larger. I also believe (but am not prepared to prove) that packed representations can, under the right circumstances, evade some information theoretic limits that constrain lossless compression, by engaging in a little honest cheating. Since you're using a purpose-specific format instead of creating a general-purpose compression scheme, you don't have to record every single bit of information in the blob itself. You can use a side channel - in the form of the format specification itself - to record some information. Which is why you see a packed representation (perhaps with optional compression) in things like protocol buffers, whereas a format like Parquet that's meant to store large volumes of self-describing data will just go straight for compression.