[fauigerzigerk]

>Start hacking about using one field for two purposes or having "special cases" and everything starts to get messy.

That advice is not as easy to put into practice as you make it sound. For instance, using one field for two purposes is often done to avoid special cases.

I think the eternal problem of software development is that both being more abstract and being more specific comes with a cost, and the middle ground is always shifting as requirements keep changing.