Except when you commit something that you don't own (such as the company you work for claim ownership), at which point all sorts of legal shenanigans commence.
This is why most large open source projects have a contributor agreement of some sort, which basically says "I own all of the copyright and patents for this thing, and you can have a free irrevocable licence to use it."
That is only the case because you have explicitly transferred those rights to your employer when you first start working for them and sign the paperwork.
Not necessarily - it depends on whether it's work for hire.
The point being that in some cases you may not have authority to grant that part of the license, and having a blanket "All your codes are belong to Zed" is potentially a good way for Zed to get sued.
