Non-accessible deck areas on yachts?

I have noticed that larger yachts have varying proportions of inaccessible, fenced off deck area. Some have tons and its a dominant part of the look, some have less and greater proportions of accessible teak decking. Why? What are the considerations beyond aesthetics? What are those areas called?

I am wondering if there are performance or regulatory considerations that aren't obvious as someone who knows nothing about yachts. I brainstormed that considerations could be:

• Aesthetics
  
• Weight (presumably teak decks rated to support lots of people and furniture are heavier)
• Privacy/quiet (maybe prevent people from walking on top of the below accommodations, maybe block views of the forward verandah's from the decks above)
• Equipment space (maybe its not completely flush with the decking, but there's actually room for essential HVAC equipment?)
• Regulatory: does it maybe only count as an "awning" rather than a "deck", and therefore allow for the space below to not be counted as "enclosed volume" for the purposes of GT rating?

Here's an extreme example of what I'm talking about with the yacht Solandge, which has huge inaccessible areas on each deck and the whole bow: