I'd like to clarify a few things to prevent misunderstandings.
No change at all of any setting will result in a different visual. All changes will result in how fast rays are being cast. You can only optimize speed, not looks in those settings.
(Apart from MSI which will decrease caustic brightness)
You can set Embree to Low quality and Fast and you will gain 1%-2% performance, as it skips coverage tests and may result in random bright pixels.
Again all only changes how fast it is being rendered or which rays get prioritized.
Everything else:
Shadow softness
Strength of bounce lighting
Will not and cannot be affected by changing any settings values.
What will change those is:
How much energy does the material consume, is there enough ground to actually reflect indirectly, scene scale correct?, Sun or HDRI softness etc.
Lastly: certain things cannot be changed without others! Bounce strength is linked to material Diffuse and how much energy it nom noms, since everything is Physically based.
However!:
You can use the Material Rayswitcher to change those individually. To get stronger GI bounce for instance. But this is not physically correct anymore.
Link to faking GI:
https://coronarenderer.freshdesk.com/support/solutions/articles/5000529341-what-is-rayswitch-material-map-