[heywire]

You might be surprised just how many successful applications simply dump a packed struct to disk as a serialization format (or even transmit it over the wire). If the operating environment (OS/hardware) is known to be of a certain type, endianness is not a concern.

[QuercusMax]

It's not just endianness; it's about maintainability. If you ever think you might change the struct, EVER, you need to worry about these things.