This question already has an answer here:
Windows snipping tool has a little "copy" button, it looks like this:
If you're composing and email in gmail, you can paste right into your email with Ctrl-V after copying from the snipping tool with that button. It's very convenient.
At StackExchange sites, I have to save the snip to my hard drive first (as far as I know). The drag-and-drop functionality you have now is great for images on my hard drive. But allowing copy paste would save me from having to save the snip, and then delete it.