If you've seen a demo of Revit MEP and Spaces or if you have used Spaces yourself then you may already be familiar with the new Rooms version of Place Spaces Automatically...called( shocking I know) Place Rooms Automatically.
This will create new rooms in all room-bounding elements on the same level with one click. It's like a shotgun blast of rooms, fill all the rooms. You'll find it on the Architecture tab > Room and Area panel > click Rooms then a button for Place Rooms Automatically will appear on the Modify|Place Room tab.
All the room-bounding elements that can define a room will end up with a room created. All the Rooms will share whatever Room Name is entered in the Properties panel when you start the tool. Their number will be increased incrementally from whatever the next available number is.
Practically speaking the Spaces version works better than this one because engineers need to create spaces where nearly all of the rooms are in the model (usually a linked model) already and the Space Naming Utility can speed up matching Space name and number to Room name and number.
If you are careful to create a list of rooms for your project in a schedule prior to having walls or at least at roughly the same time as walls are getting sketched this tool won't really help. If you import rooms from a list in Excel it won't speed up their placement because it will just blast new rooms into any valid room bounding area. It won't create rooms where rooms you've already placed are though.
If you're looking for a quick way to make rooms and don't care about naming (or other data) yet then this tool may be perfect for YOU!