Ok.... The question has been asked about previous non-believers in levels and an update.... So here you go.
Since buying my level, I've found that in the flat terrain here in Idaho... I can easily level my scope without the aid of a level, (but) when I've been out on slopes.... And the horizon is not easily in view... What I think is level starts moving off level. This doesn't seem to make any difference at closer ranges.... 400 or so yards. I suspect that on big game, even 500 would still keep me in check, but beyond that, I am pretty sure that my bullets are likely to drift out of my comfort zone for ethical shooting. Haven't been able to put that to the test yet, but I can see I always cant a little left under sloped conditions.
Also, when I am using my night vision scope, I also see this tendancy. I do a lot of hunting where the horizon is visible so I suspect that my subconscious has always helped to get me nice and vertical using that as a guide. Without that, it is definitely more challenging to stay true level. I've since put a level on each of my, favorite scopes.
As to how I find the best way to level... I place a level on my picatinny rail and then hang a plumb bob. I get the bubble level....and then adjust my scope til the vertical crosshairs align with the bob string. When both the bubble and the vertical crosshairs are perfect... I tighten up the mounts and double check as I do this. Then I mount the scope level to match the picatinny level, tighten and double check.
To be candid, my night vision yote shots are usually 100-300 yards and I don't even bother checking the scope level for these shots, however, the same scope (once I remove my night vision attachment) is also used on my 300 win mag and 308, so I can see the scope level being very useful for long range shooting.
I am a confirmed non-believer who has seen the light, but only if you are really in the long distance game at 600+ yard shooting. It certainly can't hurt to have it on for closer shots, but It might not be worth the money or bother depending on how much cant you tend to find yourself exhibiting without one.
This is why I love this forum. I'm always open to challenging my beliefs in order to improve a skill I love spending my free time engaged in. Thanks all who participated in this thread and especially those who adamantly backed having a scope level. Without that, I likely would never have purchased one... Let alone two.
James