For me, haiku is a way of capturing the fleeting nature of nature. No other poetic form seems suited so well to bringing the delicateness of the world to the page, and to illuminating the way things balance before they fall over or take flight. Or something close to both, as in this one by Issa (maybe my favourite of all haijin), translated by R.H.Blyth:
striking the fly
i hit also
a flowering plantxxxxxxxxxxxx
One thing I love about the attempt to find haiku or senryu in the world is that it’s a practice that calms, that takes one out of one’s chattering selfishness, and into the realm of the senses. It’s good for the ego to focus on details, and it makes for better writing, and better living…that is, engaging in the art of simple observation. It’s like a ritualised, literary form of meditation, to the point where even after engaging in the act and having actually come up with no decent haiku, one still feels more centred and peaceful for having tried. Or having not tried in the best possible artistic way. I don’t think we really compose haiku, I think we just notice them.
Australian Haiku Society 