To track some personally noteworthy events, observations and thoughts, letting them age and savor/regret them again a long time later.
It is a myth even before the arrival of the WWW and its entrails, that secrets are safe with anyone. Just that we are moving in hyper-speed these days that we don't need to see the passing of even a quarter of a generation that whatever covers we make of wrongs and crimes against other human persons will shit right back on our faces.
True! LKY version of this is to let history be the judge. Deng and Suharto kept secrets by telling no one.