It CAN damage your computer (or your data) but it's highly unlikely. The problem with just pulling the drive straight from the computer is that while your flash drive is plugged into your computer, it's treated as a removable drive. As such, as long as it's in the computer, data can (and sometimes is) transferred without you knowing it. Unplugging it can cause data loss or corruption. Though, so long as you're sure the active transfers (like saving a word document to the drive, or copy and pasting things into it) are done, it's highly unlikely anything bad will happen.