Hello, i have made a very deep research about using MRQ and MRG in Unreal and which setting to use to expect correct behavior from common systems like Motion Blur, Anti-Aliasing, Warmup Frames, Console Variables. Have a break to check this out if you are planning to use Unreal Engine as your render engine. This will definitely clear up your mind on what's going on, under the hood when you press render button.

ENGLISH version - 
https://www.youtube.com/watch?v=x17itF_1OaA&t=13s
RUSSIAN Version - 
https://www.youtube.com/watch?v=7VvHy47VC2g&t=170s
for professional users i have also found a very deep dive pdf from Japan authors