The biggest asset for a tablet is its screen size or real estate. If you have a 7 inch tablet vs. a 10 inch. It is easier to hold with one hand and do something else with the other. You can accomplish this lying down on couch with your head propped up on a pillow too. Tablet's are are very customizible i.e. Android tablets. You can change the size of the news article widget or the size of the calculator or clock etc. Some apps are tailor made for a tablet and offer more features and functionality than a small screen smartphone. The User Interface is alot smoother and operates a little better than some smartphones whose U.I. is 2.2 or 2.1 or lower.
I wouldn't throw away my desktop or laptop yet. I think search queries are more advanced and plentiful when you use one of these. I would trust these devices more when I am dealing with sensitive banking transactions and need that extra layer of security: Encryption that is!!! You can troubleshoot a desktop and laptop, remove defective compotents, add new ones and diagnose problems. Can you accomplish this with a tablet? I don't think so. They also don't have to rely on other things to happen before it will do what you want it to: Say you want to use and app on your phone but network difficulties will not let you use it until the congestion or problem eradicates itself. With desktops and laptops: you can have other things open in the background or playing and you can continue with what you are doing.
In closing, the tablet is better because it does not have a walkie-talkie radio or phone capability and other network difficulties to screw your experience up like smartphones do. (I know: a tablet can make calls. But they are not specifically hooked up to a carriers network to do this. You have to use a third party app) I am not saying that tablets don't have their days but the experience is much better. Matter of fact turn on your WiFi and leech of your internet router or somone elses and you will see what I am talking about. Tablets are fun. I say if you get one: I SECOND IT!!!