If you've ever needed to access blocks which lie buried behind other blocks you will appreciate the "Ghost selected block" tool which allows you to set selected blocks in the model to be semi-transparent so the blocks behind them can be selected for editing. 

To ghost one or more blocks:

1. At building level, select the building and/or component blocks to be ghosted.
2. Click on the "Ghost selected blocks" toolbar icon.

Once in a ghosted state, blocks cannot be selected and you can click "through" them to access the block(s) behind. Now you can apply any of the block geometry edit tools to the previously hidden block(s) such as "Drag face", "Cutting tool", "Add surface", "Boolean" etc, or simply navigate to the block to set attributes or add partitions.

The easiest way to "un-ghost" blocks is to Navigate to building level and click on the "Show all blocks" toolbar icon. Or for finer control you can control the ghosted state of individual blocks by navigating to them, opening the Model options dialog and on the "Block" tab check or uncheck the "Active" checkbox. This allows the ghosting of blocks to be controlled independently and can be useful for un-ghosting just one block at a time.

You can read more details on this time saver in the Program help.