On most staplers, you can rotate the metal piece the the stapler head comes in contact with to make the "arms’ of the staple either come together or be drawn apart. Why? I’ve never found the “outward” configuration to be useful.
ETA: apparently the metal piece in question is called an “anvil.”
ummm, you mean like when you’re stapling into a bulletin board on a wall?
Here’s a picture:
Nevermind…I read the OP again and realized that I don’t have an answer.
According to wikipedia:
Pinning is used to temporarily bind documents or other items, often cloth or clothing, for sewing. In order to pin using a stapler, the anvil must be shifted so that the staple bends outwards instead of inwards. The staple binds the item with relative security, but can be easily removed by pulling the staple along the plane of the paper. This method varies between staplers, as some anvils need to be simply pushed forward to allow pinning, while others must be rotated. Some staplers implement pinning by bending one leg of the staple inwards, while bending the other outwards. Some modern staplers do not even include support for pinning.
Hmph. I see. So, does anybody here actually do this?
I have done this before. Once. But only as an experiment to see if what I had been told, that the staple then acts like a pin, was true.
It was.
No.
You can’t “pin” something into a bulletin board because the prongs don’t go into the board. You staple things to a bulletin board by leaving the stapler on the normal setting but swinging the stapler open on its hinge and punching down into the board freehand.
I think cupcake, like me, misinterpreted what the OP was saying – I’d never noticed the rotating/sliding anvil thing before, so I thought the OP was asking why staplers can swing open. Once I read the Wikipedia ‘pinning’ thing above, I looked at our stapler and, sure enough, the anvil can be rotated to make the staples’ legs bend outward rather than inward. Fascinating!
Yes, I’ve used it.
It’s very handy in an office situation where you want to keep some papers together temporarily, where later in the process they will be separated or will be added-to. The ‘pinning’ staple is much easier to remove than an ordinary clinched staple.
You could also do this with a paper clip, but those are more likely to come out accidentally.
Unfortunately, it takes some effort to get all the people in the office to do this consistently. We ended up buying an additional stapler for everyone involved, in an unusual red color, setting the anvil on them to the pinning position before giving them out, and telling everyone to use only the red stapler for this process.
Wow. Do you work for the government?
I believe that’s called “tacking”.
Staplers have all sorts of fancy terminology.
t-bonham mentioned a red stapler, not a red tape dispenser. 
Nah, he works for a private company (even though they moved him to the basement). And it’s his stapler, dammit!
(10 points to whoever gets the reference.)
Too easy, Milton. And he will burn that place down.
No, a transportation company.
And if you are implying that this was wasteful spending, it took only a short analysis to determine that the employee time wasted in adjusting stapler anvils or removing clinched staples easily outweighed the cost of a bulk purchase of red staplers.
I did it by accident and was for all of a second impressed at the function when I realised what it did.
Not to mention not having the building burned down, eh?
IIRC there was a 3rd setting that would make picking a staple out even easier.
Both pins would be bent in the same direction.
The anvil on that stapler was triangular.