The Amiga computers were advanced machines meant to do all sorts of things, including file management. They had a GUI OS (Workbench) and everything right from the very start. They were not some games-only console such as the NES or SNES.
In spite of this, it lacked a battery inside of it which could have enabled it to keep the date/time when it was powered off.
If you powered on your Amiga 1200, set the date and time, then saved your file to the hard disk or a floppy disk, and then turned it off, it would have forgotten the date and time the next time it was powered on.
Only if you bought one of those "accelerator cards" that you put inside the hatch underneath the Amiga did you (typically) get such a battery as a "bonus" and were then able to actually turn off your computer.