No doubt there will be many crashes/sales on stocks. I care very little as I'm not retired, don't depend on my investments, and have years and years to wait it out afterwards. I'll continue trudging along as I always have, and will invest on a consistent basis no matter what happens.
That being said, about 1/3 of my portfolio is in bonds for the simple reason that I used to have very unstable income (photographer), which is why at the time, my investments were all in bonds in case of emergency. I have kept those over the years (ladder system, first one will "expire" in 2019), and they provide a certain amount of albeit not-necessary security.