Optimal Ratio of Disk Space and Data Transfer

I'm not sure if this has been already discussed before, but I'll ask anyway: what is the optimal ratio of disk space and data transfer for hosting accounts?
We've all been there, mix and matching different features to appeal more to prospective customers. And in spite of the current trend of insanely "giving away" unlimited disk space or unlimited data transfers (or both), there are some hosts that are sane enough to offer realistic packages.
So there is my question: is there any optimal ratio for the two or it's really just anything goes, let the marketing guy pull his stuff?

A rather common disk space to data transfer ratio is ~1/10. As to why that is the case, it's anyone's guess. I suppose it's got to do with real world constraints, marketing related reasons, and to an extent, history/legacy.
Quote:


let the marketing guy pull his stuff?


Yeah, once a certain account dimension limit is breached, I suppose you can just let the marketing guy set them. They lose their real meaning.





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