The 600 samples in my example are not thought to render up to the end. The idea was to let it render for a certain time, then cancel the render. Usually, I use 35 to 40 samples for clear images. Often, I just let it render (in progressive mode!) and just cancel after a couple of hours if I see that no grain is left.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.