[raverbashing]

"pretty dangerous for post-hoc analysis because if (when!) something goes wrong, the information is overwritten and gone forever."

If your last active time table is being fumbled then yes, but I'd worry about all the other parts of your data if that was the case.

Dangerous is not something I would ascribe to a "last active time" table (except if you're using it for security audit purposes)

[vedang]

Mutable data does not give you any ability to analyse actions over a period of time. For example: "How many people were active during the month of the Indian Elections?" Can't tell you today, because all the data has been mutated away.

Secondly, mutable data also means that you have less scope of drawing new insights from historic data. (Primarily because you never have historic data)