What can you do when the power on black ops is turned on?

Answer 1

There are a bunch of things-

You can buy perks (they're the vending machines. JuggerNog, Quick Revive, Speed Cola and Double Tap.)

You can use the teleporter (have to link them first.)

You can use Pack-a-Punch (upgrades your weapons. Cost 5000 points)

You can use traps (cost 1000). Kills Zombies that walk through no matter what round.

Sometimes a door opens when you turn on the power, for example, on kino der toten in black ops, when you turn on the power, the stage curtains come apart.

Also, sometimes new zombies appear when you turn on the power. In black ops, nova gas zombies appear when you turn on the power (known as gollums.)