Related Questions:
Event Diary doesn't show that event has been booked
Show excluded spaces
It does not seem to blocking the additional rooms?
Is there a way that the other rooms are grayed out
Answer:
When you look at the Event Diary, there is a checkbox to "Show excluded spaces" if you select this, it will show grey slots for Spaces that are blocked by another Space.
You have the ability to have this pre-selected by default if preferred:
Click on Settings -> Organization Settings -> Other Settings
Select the checkbox Show Excluded Spaces -> Save
