Some people blog for commercial purposes. Others to document. Some others blog because really, they have meaningful things to say.
Me, I blog because it serves as my diary. In a click of mouse, I can recall what I was thinking of 3 years ago. The blog is available anytime, anywhere I want it (with internet access of course). Some people may Facebook, Twitt, or Instagram - but I think I will stick with my old fashioned blog.