Squisher, to find literature on the forces at play when using a block, other than what I say, try TCIA Best Practices in rigging or things like that. Or I'm sure others like Gerry B or maybe Tony from North American Training Solutions or someone like that can chime in.
The amount of friction at the rings is going to vary from what size ring, what size rope, how many rings, etc. So, in my diagram I just guessed at numbers. In the real world, there is a difference and it is evident.
If you are use to blocks and how things react when lowering for years and then you use the rings, you will see the difference and like it.
It is significant.
With multiple rigging points using rings, my groundman rarily goes beyond one or two wraps on the hobbs or grcs on large limbs or logs. Where.... we use to do 3 or 4 wraps with blocks.