Our 1st generation Nexus 7 tablet lives underneath our sofa. I originally put it there to use as the TV remote for the Chromecast, but I find myself simply using my phone. Since my phone is perpetually in my pocket or within arm's reach, it's even more convenient than trying to reach underneath the sofa to unplug the tablet which is perpetually charging. I also thought I would use the tablet to play games on, but once again I find myself doing that either on my phone when I have a random minute somewhere or on my PS3 when I have more like an hour to game.
I have always viewed tablets as a information-consuming device, not a information-producing device. You can quite comfortably browse the web, read emails and books, watch videos, etc. But beyond writing short emails and such, chances are you are not going to be writing a blog post or novel on one. And that's totally fine and a reasonable position for a device to be in.
But that's the same position a smartphone is in as well. And compared to a tablet, a phone is fully portable and an actual phone. For a laptop you have the information production capabilities that win out over a tablet. So a tablet is not as portable nor has all the features of a smartphone while not being able to produce content like a laptop. Basically tablets are getting squeezed out from both sides of the portability/versatility spectrum.
The only person I know who uses a tablet regularly is my father-in-law who doesn't have a smartphone or a laptop (but does have a desktop). In that situation a tablet makes sense. But if I managed to convince him to actually switch to a smartphone with a large enough screen or a Chromebook then I don't know if he would continue to use his tablet.
I should admit that I use my tablet on every flight I take. I will play games on it as the larger screen is nicer than my phone for long-term gaming (although because of the typical lack of cloud saving in games for your progress they are games I only play on my tablet). Otherwise I will load movies on my tablet and watch those on the flight. But unless I'm a trapped audience on a flying cylinder in the sky I just don't use my tablet.
I suspect with most people, the usefulness of a tablet in day-to-day use comes down to whether you have the largest phone or smallest laptop that makes you happy. For me that's my Nexus 5 and MacBook Pro, while for my wife it's her Moto X and Samsung Chromebook. For each person the correct phone and laptop size will be a personal choice based on hand size, how much weight they are willing to cart around, minimal screen size, etc. But my suspicion is that if you can get a phone and laptop that make you happy you won't have a regular use of a tablet.
Even if you try to consider in an e-reader, the proposition for a tablet doesn't really improve. I still find e-readers easier to read on, more portable, have better battery life, and are cheaper. So skipping an e-reader for a tablet only makes sense if a tablet makes sense on its own merits.
In my mind, unless you are a frequent flyer in economy or are lack a smartphone/laptop, owning a tablet doesn't seem to pan out anymore. The days of a tablet of being an attractive purchase seems to have passed for the majority of people.