The fact is, they cut things really well.
Anything that can reasonably fit between the blades will get cut. If it's too big, you can't get enough leverage to get started, but anything smaller than that is fair game. As a rule of thumb, if you have to open the blades more than 90°, you're not cutting it. You could cut a high-tension wire, but you couldn't get enough leverage to cut a car in half.
The weird thing about the shears, though, is the fact that they cut things that aren't supposed to be cut. Like emotions. If you cut your hair with them, you'll always feel better about the new haircut, because you simply won't have an emotional connection to the old one anymore. Cutting that high-tension wire will always feel cathartic, because it never should have been together in the first place. The new state always seems more natural than the old one.
That's not the only thing, though. If you cut up a book, the new book seems more pleasing than the old one. Nobody knows how far this effect spreads, although if you decide to play William Burroughs and use the cut-up pieces to make a new work, it'll probably be well-received. (Maybe it's possible to drive a popular book back into obscurity this way. Or maybe only the person holding the scissors will think the new version is superior. Or maybe only the author loses the emotional connection. Who's to say?)
The most disturbing usage of the scissors, though, is with modern photographs. Cut up a photograph the right way, and you can make someone uncomfortable in their own skin, because they no longer feel the same connection to how they look at they used to. Or maybe they think one of their features is now extraneous. Maybe you'll drive them to self-harm, because that part needs to leave. Or maybe they just grow lethargic and apathetic about it, they just don't care.
And of course, if you cut between people in a photograph, they'll lose their emotional connection with each other. Maybe someone will use this to make enemies not hate each other so much, but it's always more likely that some vindictive sort will make lovers drift apart. It's never a sure thing, and some people can resist it, but it's still going to make for a rough time in your life when those whom you hold dearest now seem distant and alien.