Just trying to understand why when Portals was implemented in 2.75, nobody doubted the advantages of this with respect to the lower noise (no lower render time). The advantage of Portals was clear in many user tests, obtaining much less noise. But then in new versions of Blender some users began to question the advantages of Portals in some interior scenes.
The think is that in 2.75 default scenes were set in World tab by default: Settings > Multiple Importance=OFF (Map Resolution=256 if you enabled it). So I think that many tests by users when Portals was implemented were done with Multiple Importance=OFF.
Then from Blender 2.77 that configuration began to be by default: Multiple Importance=ON and Map Resolution=1024.
Then in master (2.79 and 2.80) Sampling methods were implemented: Manual, Auto, None.
Edit:
Some tests in 2.76b (CPU):
*No Portals - Multiple Importance OFF
*Portals - Multiple Importance OFF
*No Portals - Multiple Importance ON - Map Resolution=256
*Portals - Multiple Importance ON - Map Resolution=256
*No Portals - Multiple Importance ON - Map Resolution=1024
*Portals - Multiple Importance ON - Map Resolution=1024
Scene:
portals_2.76b.blend (1.4 MB)
Edit 2:
Do you know what the equivalent of setting Multiple importance Sampling = OFF would be in 2.8?
I can only see the new Sampling methods in World tab. So setting “None” would be the same thing?