Battery backed memory is required to keep track of time and other erasable BIOS settings in a computer system. Without it it would probably be unfeasibly difficult to reset the BIOS settings on a motherboard should an issue arise with boot settings or other down to the metal adjustments. Should the CMOS which contains the settings become corrupted, all you need to do is unplug the game and remove the battery, then do the opposite.

The same can be said for older generation board sets where the CPU relied on AA batteries to maintain the contents of system RAM. Without batteries, back then if you play a game and you notice an issue with a setting in the service menu or a high score had gotten out of whack, you would probably have to pull the RAM chip and either blank it or swap it with a blank one. This would create the need to include socketed memory, which would cause more potential points of failure since you are dealing with plug-in connections on the board as opposed to directly soldered ones.

Now we have NVRAM which is more reliable and cheaper these days, but it still means the CPU loses track of time so special features like the Twilight Zone clock and midnight madness will not work.

It's rarely something you have to worry about, they last years.