To follow up on this, I recently implemented a packed vector format. As a LE advocate I surprised myself by ordering the packing in BE order — because that let me simply byte-compare vector encodings to compare the underlying vectors, which was a huge performance increase.

Data structures which are frequently compared, e.g. to be sorted, benefit from BE ordering. Just binary compare them as byte strings, usually an efficient inline operation.

If I were implementing a packed wire format for SQL data, for example, I’d probably do it in BE order.