No real use? Let's see... I find my smartphone very useful for browsing the net in places where there's no space for laptop. You can also stand while browsing, which is hard to do with a laptop and an extremely convenient feature. Also, if you own a car mount, you can use it as GPS. This can be very useful if you travel by car a lot (or just have zero sense of direction, like my mom

) or even just don't like carrying map around. I own one of the smallest smartphones on the market (and probably the smallest you can get with a physical keyboard), so it's infinitely more compact than a paper map could ever hope to be. Aside from that, I often use it as a flashlight. The camera isn't really great, but it works well enough, and if you need to take a quick snapshot of something, it's awesome. Also, thanks to the physical QWERTY keyboard, it's also convenient as a notepad for writing down stuff without the need for neither a pen, a piece of paper or a hard surface to write on. Comes with a calendar and a reminder system, too. And there's probably an app that would allow it to work as a graphic calculator, hopefully saving me quite a bit of money. Finally, it works as an alarm clock. And a music player, which is great on long bus trips. Oh, and before I forget. It can be used as a regular phone and does this job quite well.
Yes, there are dedicated devices for all this, and they do the job better in most cases, but my smartphone fits it all into a single device I can carry in my trouser pocket (or even a waistcoat pocket. That thing really is
tiny). Perhaps other, larger phones are less convenient, but the case still stands unless you're not wearing a jacket. It replaces a lot of stuff that would otherwise I'd have to carry in my briefcase/jacket pockets. While it's no substitute for a proper laptop, there are places where I wouldn't be able to get a laptop out of my briefcase, nevermind open it.
I can agree about a tablet, though. The entire reason why smartphone is so great is that it can be really dinky. In my case, it's only slightly wider and about 1.5 as thick as a regular phone. Others are larger, but still small. Tablet is as big as a netbook (so no pocket carry unless you're wearing cammies, and even than, it's a bad idea), while not really being able to do anything a good smartphone or a laptop can.