What about micro missiles with AI? A big boss shooting 100x of them with 10 variations, You can waste 2 lines of code to implement what happen with every missile when they launch (a smoke can popup on his cannon) and 2 lines to setup what happen when they hit the player, instead of codding 20 lines of the same code.
Another sample, when you do moving platforms like in Mario, instead of doing 10 lines of code for each type of platform (sprite and size), put them on a Families and setup this families to be a platform.
And the last sample. Making a "Cobra" game, you'll need to setup his ammo types, draw them, put them inside a Families, write a code for that Families and only setup what is different between each other, like the amount of life that specific ammo hurt the enemy.
You can setup everything one by one, but you'll agree with Ashley and the Community when you start to do many enemies and your code start to make you lost inside each repetitive codes.
To make sure the greatest of Families, you can figure out a planetary game. You setup each planet, setup his families, and them, put all the cities and spaceships, asteroids, everything you need inside families for that planet. When you kill that planet, you can setup to clear all his objects instead of clear one by one, free of risk to bug your game.