Look, there is risk in any PE. Thats why we spend so much time here trying to educate our members about their members :) . Seriously though, learn enough to reduce the risk when doing PE.
So, in clamping there are basically three levels.
1) partial restriction of outflow of blood. At this level the clamp will still slide and you get very little discoloration. This is low pressure clamping.
2) Stopping of outflow of blood, but you can still kegel in blood. The clamp no longer slides. You will get darkening of the penis as oxygen levels begin to drop. This is moderate pressure clamping.
3) Stopping of outflow AND inflow, you are unable to kegel in blood at this level. Clamp doesn’t slide and you must release it a bit to be able to kegel in blood. At this level its important to not exceed 10 minutes due to hypoxia. This is high pressure clamping.
What you describe would fall in low pressure clamping, and it basically reduces outflow of blood, but circulation continues. It is ALWAYS advisable to monitor your dick if you have any constrictor on it, and be safe.
I think for some guys with a high percentage of elastin in the tunica, it may be enough pressure to create expansion over long periods of time. For most guys, its not enough pressure to create expansion, but is useful in HOLDING an expanded state from higher pressure clamping and may be of benefit that way.
If you wish to use cock rings for prolonged periods of time, make sure you check carefully as you extend the time to make sure that you are not killing your dick. Further, watch your EQ carefully in that for some guys it will act as excessive stress and push you into over training. Some guys with tough dicks will find it may actually enhance recovery and accelerate girth gains.
You really have to try it, in a very careful way and see how it effects you. DO NOT try sleeping with it until you are POSITIVE it doesn’t cut your circulation to a dangerous level. Even then, I would set my alarm for an hour, then 2 hours, then 3 etc to check and make sure nothing bad is happening. Remember you can roll over face down and create a blockage that might not occur face up. Risky business that most shouldn’t attempt.