I read somewhere in manual that Display → Custom Render Settings are only for display purpose - not final rendering. But I noticed that SPP has great impact on final rendering - better AA quality and much longer render time.
I didn’t tested other settings like GI, Roughness but are you sure that it works like described in manual ?
I think you have misread the manual.
The custom setting clearly is designed to impact the final rendering and yes it significantly adds to the render time and also way higher quality and detail specially for lighting and reflections.
Right, this info is little misleading
because Custom Settings is in the same window that Display → Preview Quality.
Shouldn’t it be in render settings instead ?
Also if it affect final rendering it should be global with copy-paste between different scenes to have the same quality for all scenes.
I found detailed info here, strange place :
