For example, in Plants vs Zombies, the zombies come in waves. If I recall, there's always at least two waves. The first and easier wave and then when you get 90% through the stage there's a "final wave" which is shorter, harder, and has a bunch of zombies all come at once.
My question is, why would a game decide to announce when you change from one wave to the next? They could have just let the level progress from start to finish without this if they wanted to.
Does this make the game more fun for some reason? Where can I learn more about this technique (eg: does it have a name)?