Every time I switch the source for my project (between sandboxes or between production and a sandbox) it defaults to "Work Online", and I need to remember to switch that or else it starts deploying things willy nilly.
I'm using version control, so I want to be in control of what's on the server and what's not. I think I may have accidentally saved something to my production org because I didn't remember to uncheck that (there's a deployment with a random hash name that says I deployed it).