Sometimes, when you're having an online conversation with someone, you want to show them a picture of what's on your screen.
If you find yourself in this situation, you have a few options:
Video screen share over Skype or Google+ (handy if you're already connected using one of these, but Skype charges for that now, and you probably weren't already using Google+)
Take a screen shot and email or otherwise fileshare it to them (thus filling their inbox/Dropbox/etc with an image they probably don't want to keep)
Save an image and post it on Facebook (but your other 814 friends probably don't care to see it)
So you certainly can share an image of your screen, but it will probably be an obnoxious process.
Here is another- and, I posit- better way to share a simple image of your screen over the internet.