Sorry for the late reply. Yes, most useful indeed.
I have a couple of questions left now, pointers to documentation are still welcome
If a snapshot is a point in time and is there to allow us to go back to the time of a snapshot...
After taking a snapshot:
1) If I want to run a test, do I run it on the original LV or the snapshot?
2) How do I use the snapshot to return to a state before the test was made (time of snapshot).
What I did was, snapshot, mount snapshot instead of original LV, if ok, remove snapshot and do the same on original LV... but it seems all wrong now.