If you don't have one then I do suggest you run to the nearest craft store with a few dollars and some spare change in your hand because they are fairly cheap, but pack a big punch (corny joke intended).
I use it to snip the corners of student work before displaying them and it gives a really nice finished look. I use in on my signs. I use it on labels.
It's handy dandy and addictive. You'll never have right angles in your room again.