We were recently implementing a new UDP network protocol implementation, speaking to an existing device, and the documentation merely said "one byte for the station id, one byte for the message type, two bytes for the payload"--and then listed eight possible payloads.

And we built something that packed those numbers into 8-bit and 16-bit fields and sent them and it didn't work. And we're wondering why it needs two bytes for something that's only reached eight. That's a lot of headroom.