Previously (almost) all buildings had a building clearance that prevented you from building them into each other. Now individual Buildings encroachments will have a specific Build Clearance Type (Soft, Hard, Complex). 
Buildings with Soft Clearance are cosmetic and structural buildable's as well as Conveyor Belts and Pipes, and they can now be built overlapping with any other buildings to give you more freedom when designing and building your factories, either for cosmetic purposes or to make even more compact factory floors. 
Buildings with Soft Clearance can intersect each other and buildings with Hard Clearance and Complex Clearance.
Whether your buildable's clip through each other or not is entirely up to the individual player and if this is something that bothers the player they will still be notified by the game when Soft Clearance clipping occurs via an on-screen build warning and a new hologram color signaling those buildings are overlapping.
Buildings with Hard Clearance are all buildings that have functionality such as Constructors, Assemblers, Power Poles, Splitter, The HUB, etc. They will function largely as before and cannot be built overlapping with each other. 
Buildings with Hard Clearance cannot intersect each other in any way.
Some buildings with Hard Clearance will also get Complex Clearance, allowing buildings with hard clearance to be built within the hitbox. 
You will now be allowed to construct Buildings / Machines in areas that you previously were prevented in doing so within another Buildings bounding box. This means that the "free space" within a large Buildings can now have other smaller Buildings / Machines built there.
Buildings with Complex Clearance also have Hard Clearance. but instead of being a "encroachment box" surrounding the whole Building, there are now several bounding boxes surrounding only key parts, hence the term "Complex Clearance", leaving the "free areas" open to be used.
The Buildings that have Complex Clearance are Coal Generator, Fuel Generator, Nuclear Power Plant, Freight Platform, Empty Platform, Train Station, Refinery, Particle Accelerator, AWESOME Sink, and Space Elevator 
Hologram Color for both Soft Clearance and Hard Clearance can be set in Settings.
Complex Clearance has no specific Hologram Color setting and uses the same setting as for Hard Clearance.
- Patch 0.5.0.0
- Undocumented Change - Added Color Hologram Settings for Building, Dismantling, Hard Clearance, and Soft Clearance.
- Undocumented Change - Added Complex Clearance.
- YouTube - Dev Vlog: New Build Pieces and Build System changes coming to Update 5 - Build System Change: Introducing Soft & Hard Clearance
- YouTube - September 7th, 2021 Livestream - Q&A: Will Splitters & Mergers have Soft or Hard Clearance?
- YouTube - BUILD SYSTEM Changes Coming in Update 5 - Modify hologram colors
- YouTube - September 7th, 2021 Livestream - Q&A: Why is Power Pole considered Hard Clearance?
- YouTube - BUILD SYSTEM Changes Coming in Update 5 - Complex Clearance
- YouTube - BUILD SYSTEM Changes Coming in Update 5 - Complex Clearance Buildings