Why should I write a personal diary?

I just restarted writing my personal diary 4 days back. It was while talking to my younger sister, Kruti, (yes, the Quora celeb) that I suddenly realised I should start writing my diary again. I don't know what prompted it, more of a self-realisation, I guess. Or maybe wisdom from the company I keep (rather, had at the moment)? 

This is more like a note to self, than for the readers.

Now, like a obedient class 7 kid, I will write the answer.

I should write my personal diary because :

1. It gives me a chance to reflect on the day's happenings & my reaction to them. It should help me, should I choose, improve my Sambhav & help me become a better human being with control on my emotions & my actions & reactions.

2. I write about the positive things mostly which helps me keep a positive view towards life.

3. Writing my diary gives me a chance to read it which gives me a third person's perspective on my life & me, which helps me evaluate myself & correct my faults . At the least, it can help me to not repeat my mistakes.

4. At t=t, it will become a memory should I choose to recollect & read it.