What a bizarre thread.
A desktop is useless as its too big
A laptop is useless as its less powered, small screen
A tablet is useless as its less powered, small screen
A phone is useless as its less powered and a tiny screen.
In various use cases, one of the above is near perfect, whether you need power, screen size, portability. So, if you have a use case for each, you own each.
Same applies to a small fridge, medium fridge, large fridge, same goes for cars.
To state that a device is useless is silly and short sighted.
iPads sell. iPhones sell. Imagine if you can buy an iPad for $99 on contract?
I have an iPad Air, 128, Cellular. Do I use it heaps? No. But when I use it, its ideal. Im not carrying my rMBP outside to have a quiet one in the sun, nor to hospital where I was for a week a while back. iPad perfect. Do I sit here in my living room typing this post on my iPad? No, I am on my rMBP. If you have a use for a device, use it, otherwise no need to buy.
I personally feel a phablet is too big for a phone, and too small for a tablet, but many like it, so while its not me, its also not useless.
I think the point a lot of people are making is that a tablet is the luxury item here. It is the first one you could happily cull from your list of devices and not really miss at all. It doesn't do anything whatsoever that either a mobile phone, or a laptop can do. It is less portable than a phone and less powerful than a laptop. It's no more portable than a notebook/small laptop and it isn't as useful. For the vast majority of people, it just isn't all that necessary. Who here; if they own a phone, a laptop and a tablet, wouldn't hesitate to lose the tablet if they had to be without one of the three devices on a permanent basis? That says it all really. Sure there will be people who have kids and parents who couldn't possibly operate without their tablets, but for the majority of us it's a luxury item.
Also, who here would own a tablet if Apple didn't make them? How many here bought an iPad purely because they're suckers for Apple products? Would you bother with a Samsung tablet if that's all there was available? Doubtless most would dismiss the Samsung tablet as a 'pointless product' ;-)