When I need to comply with a specific binary format, I never rely on Binary/Serialize class instances - I always fall back on the primitive operations on Words of varying sizes (perhaps defining my own type classes for convenience). The 'Builder' type makes this pretty easy.
If I were writing binary data to disk, in my mind that would fall under "complying with a specific binary format".
Indeed, and I was starting to do that... well, I would make my own project specific Serialize class, since the type dispatch is useful. But copy pasting a UTF8 encoder, or the variable length Integer encoder, or whatever seemed kinda unpleasant. Surely we could expose that stuff in a library, whose explicit goal was that they *would* remain compatible ways to serialize various basic types, and then just reuse those functions? E.g. that is already done for words with the putWordN{be,le} functions, and is available separately for UTF8.
I do, however, rely on the SafeCopy class (or the equivalent Happstack.Data.Serialize class) to be able to read it's own data back from persistent storage - it is a specific design goal of the library
Indeed, I also wound up inventing my own versioning format, which looks basically the same as safe copy, except much simpler, I just put a version byte, and then case on that for deserialization. However, I only put the version on things I have reason to change, and that doesn't include built-in data types, like Integer or String. So it's all my own data types, which I control the instance declarations for anyway, so I'm not really worried about those.