They are useful so they can spawn ever mob like skeleton,creeper,blaze,pig,etc we could make cool maps and fighting areas and xp traps with this block please answer very imoportant block that should be added because there will be no mods anytime soon?
The Meaning of Life, the Universe, and Everything.
As much as I would like to be able to place spawners, I can see that not being on their top priorities. If I wanted something that wouldn't require 4J to do a lot of work, I'd want to be able to push spawners with pistons. That way you can join spawners and make big XP farms without the negative effect of crashing the game in creative when someone spazzes out.