The market for gaming PCs may be strong (and many of those are not in the statistic because people build them on their own) but in general, desktop PCs are pretty useless for most people nowadays. Except for companies who let their people work with it on their desk or schools who have PC rooms. I guess that's where almost all standard desktop PC sales come from.

You can also use a PC very long nowadays without many problems. Buy a PC and use it like 10 years for pretty much everything you need it for (except gaming and professional usage)

But tablets are also useless for many nowadays. Smartphones got bigger and bigger and most are like 5.5 inch nowadays. Enough for most people. In the past people used it for stuff like Netflix but they can simply stream it on their "smart TVs" nowadays.

I wonder how the smart watch market looks like. That's also something I find useless except for a few things.  

I knew from beginning that tablets were just kid toys but analyst companies didn't hire me.

Both markets are still falling, with PCs apparently reaching a stability point. But it's a pretty poor comparison since tablets were killed by 5'+ smartphones.

Tablets appeared in a time that smartphones had 3.5 to 4' screens. After some time, phones with 5' start to rise and people decided that the compromise of having a slightly smaller screen and a huge phone was better than carrying 2 different devices.

But it is not like people will stop buying PCs altogether. The crowd that only did basic browsing jumped to phones. Right now, the remaining users are the ones that have to create content, develop or simply write a lot of stuff on Office suites. If smartphones manage to do this work (maybe a dock like the S8), then we can see a sharp decrease on PCs again. Otherwise, things will stabilize.

I think they are 100% useless. Their only function is to avoid you taking your phone out of your pocket 50% of the time. In the other 50%, you will look at your watch and think "well, I have to get my phone to answer that". It's a poor excuse for a 300 dollar device that ends up being one more thing to charge daily. And, of course, you may end up with a dead battery in the end of the day, so it will do less stuff than a regular wrist watch.

They do some health monitoring stuff, but I wouldn't count that since we have smart bands doing the same for 10% of the cost and with 10 times better battery.