I had a reason for writing those, but now I can't remember fully.

Hmmm.... Think it had to do with need for archiving and growth planning (how long). OLTP or decision support (ie, do we need to consider storing pre-computed averages, selective denormalisation, etc)

But those are more advanced concepts in DB design, and one of the biggest mistakes I see is people skipping intermediate steps to get to a final design.ie not bothering to normalise fully.