Well, for instance, for roughly a year on my Macbook (2014 Retina 13"). It gets in a state where the keyboard and trackpad are unresponsive but the laptop is clearly still running. USB devices are probably hosed too, because attaching an external keyboard at this point doesn't help either. Started with El Capitan, continues with Sierra, and Apple support finds all hardware diagnostics are okay. My only recourse is to power cycle the laptop.

Another example, once or twice a week when waking up from sleep the wifi adapter doesn't reattach, and hovering over the wifi status in the menu bar yields a beach ball. My only recourse is to power cycle the laptop.

About a year ago my Plantronics bluetooth headset stopped reliably pairing, or rather it does pair, but the audio quality is so horrible I gave up and went back to wired earbuds.

So yes, far from perfect. I would say the product team has been distracted with convenience frills like Handoff, AirDrop, auto-unlock via Apple Watch, and so on, when what I would prefer is reliable sleep/wake and i/o devices that work every time.

Nonetheless, this is still leaps and bounds ahead of the Windows 7 laptop the corporate office insists I use. And it's a reputable brand and everything, and not a fluke (they've swapped out the laptop multiple times but every one has some fatal flaw.)