[_____s]

On some level, that is true, but when it comes to performance reviews and such, as the post mentions, it is very easy for your manager(s) to forget some specific things done over a period of time, forget their impact, etc. Even you may forget specific things that were done in a, say, 6 month period.

Besides that, it's also a good reminder for your own self to recap the work you've done in a specific period of time, notice your growth (or lack of any growth), etc. I've personally seen pretty good results with a similar approach.