46% is the defautl if you are using the Final setting. Some people don't go above 39%. Like all settings people have different ideas. I think it was at the time of Vue 6 that people did testing. I can't remember whether it was on this forum or the registered e-on forum and found that you don't have to go above 39%, for example, to see any quality improvements.

As I said, different people will have different ideas. You just have to experiment and try what others who know a lot suggest.

I use varied settings. If my work is very complex as to textures and functions and is slower rendering for the size of the image I have set, I cut down on some of the areas that use more time as well as check my quality settings in the atmosphere panel. I usually don't like to go over 12 hours because now I have simplified my life and have one fast desktop and a laptop so I render at night. Normally they take from 4-8 hours. If , when I print it, the final print looks good to me, I am satisfied. As I mentioned in a previous post I use software to get my final size for 13 x 19 inch paper.

A lot depends on how you will use the final image if you are talking about still images. There is no absolute  "right" way for everyone.  There are guides which many people over the years have posted. Do a search under rendering and compare the information and then experiment and find what works for you.