Unfortunately, it's not so great at that. I have an HTC Desire (Bravo in the USA) that still works and I'd like to reuse as a SIP client. Unfortunately, it only runs CM 7.2. That would be fine if it were a patched version, but the latest nightly build was 2013 and that's so old that it doesn't contain an up-to-date certificate list or an SSL client library that supports modern versions of the TLS protocol, meaning that you can't use it for anything network connected.
Sure, the device is pretty old, but it has a 1GHz CPU, 512MB of RAM, and up to 32GB of flash on the SD card: that's ample for a lot of uses (it wasn't so long ago that I was using a desktop less powerful!) and throwing it away seems horribly wasteful. It was launched in 2010 and the last release (not nightly) from CM was 2012. That's less long-term support than Apple gives for iOS devices and Google gives for Nexus devices. Unfortunately, there's not much money to be made in supporting hardware that the manufacturers consider to be obsolete.
The problem with this computer that you wear on your wrist is that it doesn't do most things that I expect my computer to be able to do, is even worse for input than a phone, and the couple of things that it does do very well (tell time, show notifications, fitness tracking) are better done on a watch, a phone, and a fitness tracker.
My analog wristwatch is very highly legible, silent, accurate, and can withstand the elements and dives up to 300m. It is always visible, can be easily glanced at by someone across the table if they need to tell the time, and it rarely, if ever needs any kind of attention.
When I get a notification on my phone, I look at it, tap the notification, and can act immediately.
Get a notification on a smart watch and you have to look at it, then take out your phone, tap the notification, and act on it. The smart watch adds an unneeded extra step.
Fitness tracking was supposed to be the "killer app," but fitness activities are often both rough-n-tumble and happen outside in the elements. For that you want the cheapest, simplest device possible so that when you inevitably have to replace your destroyed one, you're not paying through the nose again (not to mention also losing your timekeeping for the period during which you are replacing it).
All this plus they are very high maintenance, needing to be charged all the time, limited in life span, and needing software updates from time to time, as well as the often finicky pairing with a phone—and the fact that there's not a single thing that I regularly do with my computer (or even phone) that I'd like to try doing on that tiny screen—and the fact that you can't even hack it to be used for low-input/low-output situations (say, embedded applications—not to mention the ridiculous cost)—and it's just not much of a wrist computer either.
Nope, I'm just gonna stick to my regular wristwatch, phone, fitness tracker, and computing devices. If I need mobile computing, a 5" Android display, octo-core CPU, and 32GB storage are already more than cramped enough.
It's really hard to come up with a scenario in which the problem that leap seconds solve actually exists.
You had mail, but the super-user read it, and deleted it!