ALWAYS buckled. Here's a good example of why as well......
If you're wondering, only the GoPro snapped off. Helmet, although bells were still rung, stayed on nice and tight and spared me from more serious injury.
Of course I buckle it! Why bother spending that kind of cash on a helmet if you're not gonna buckle it? Might as well just wear a hat in that case! Let natural selection thin out the herd...