On 10.10.2, several times a day, I hit F3 ("Mission Control"?) to see all my windows, in order to quickly navigate to one.
And I notice empty desktops keep getting created:

I know I can hold down the option key, to get the X on each of them to more easily delete them one at a time. But this can still take a while. I've seen it get as high as 112! 112 empty desktops?!
Why are they created in the first place? Is it some keystroke I don't realize I'm hitting? Do they not consume system resources?
Can new desktops just be permanently disabled, leaving me only ever with desktops which actually correspond to my screen and two external monitors? (I've frankly never understood the point of virtual desktops anyway.)