If you plan your layout right you can make all 100 levels in one layout it just depends on the type of game you're making and what you need it to be like.
For example you can have groups of logic dictating the behavior of enemies, the player and even power-ups or items depending on a global variable that carries the current level.
Also the sprites have to be in the layout so if you use "re-usable sprites for items" in which each frame contains one image of a different item you can spawn them as needed and have them change to the correct frame on command.
Again it depends on the game your'e building and your current needs. I did that for FreeFall Bird. I have only 3 layouts. one of which is the actual game while the first is just the intro screen and the other is the credits screen. Everything else is handled in events.(lots of carefully planned events i might add)