When for example a command block as FallingSand falls next to a block providing a redstone signal, it won't update.

/summon falling_block ~ ~2 ~ {Block:stone,Time:1,Passengers:[{id:"falling_block",Block:redstone_block,Time:1,Passengers:[{id:"falling_block",Block:command_block,TileEntityData:{Command:"say Test"},Time:1}]}]}

When you place a block next to it, it will say "Test".

Note: It appears that this only affects block entities. Here are some examples:

Affected blocks:

• Dispenser
• Dropper
• Command block

Unaffected blocks:

• Rails (Activator and golden)
• Redstone lamp
• Piston