system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Safely eject USB key feature on desktops.

How does it work?
gpt
In the days of yore, USB drives were slow. So if you needed to work on a file on a usb, the file manager would do a little trick. When you hit save, it would save that file to RAM really quickly so you could get working again quickly instead of waiting 30s for a file to save. Then while you were working, it'd slowly transfer that data to the USB drive in the background. If you pulled out the USB while that background transfer was happening, you'd end up with a corrupt file. Safely Ejecting basically makes sure that all the data transfers are done before it says it's safe. It's not as much of an issue now that USB 3.0 is the norm; larger files never went through this background process, and smaller files take almost no time to finish.