For the most part, terminal is never used in UFO 50. There are some cool codes that change games somewhat but they are fairly insignificant I'd say. Just a fun gimmick.

But there's more to it, of course!
If you watch the Night Manor's credits til the end, you will be rewarded with a code: GREG-MILK! But, entering it in the terminal doesn't launch any game - instead the usually incomprehensible text to the right forms an obscure message.

Congratulations! You're stepping into a big meta puzzle encompassing almost every UFO 50 game. But beware - to solve it you need to have some basic understanding of every game included in the puzzle (and, since you can't know beforehand what games will be included, you really need to play every one of them a little bit...).

Good luck on your journey through this mystery if you wish to embark on it.