System Information
Operating system: Ubuntu 18.04 64bit
Graphics card: AMD RX 580 (8GB)
Blender Version
Broken: 2.80.49, cc5bdf029324, 2019-03-16
Short description of error
As you say yourself, this is not a bug, but different defaults.
Opening old files with certain clamp values should not, and does not change or override the clamp value. I just tested this, and it does not happen. If you experience this, it is a bug, but in your report it is not quite clear if you are having that particular issue or not.
Nono, the clamp value remained 0 from Blender 2.7.
It was an intentional change, I don't think it's better overall to go back to 0.
D2769: Cycles: change defaults for filter glossy, clamp and branched path AA.
Also, exposure -6.781 is a really extreme value, would not recommend to use that in practice.
Brecht, you wrote it, "in production files the clamp is enabled".
Most work i do is not for a short film, i do still images and having Clamp 0 is necessary. By the way, you said you set it to 10 because of noise, well i don't think it is the case since there is the Denoisier. And anyway having it set to 0 as default could prevent people with no experience to see weird results.
I have exposure -6.781 there because i'm dealing with real world Sun and Sky values such as 700 of strength for Sun and 60 for Sky. Since the measurement unit of the strength value is W/m2
Also for still images do people overwhelmingly use clamping, and it's standard in other renderers to enable it by default.
Clamp still helps significantly even when using denoising.
If you're going to adjust exposure then you should simply adjust clamp accordingly too.
Then what about the caustics enabled by default?
