To pick up the ethical debate away from a conditions thread:
On Monday when I went up Cwm Lloer the conditions were not perfect, but were good enough so that I didn't need to do any harm to any vegetation etc.
Considering the ongoing debate, I think that there are many considerations in making the division or not and I don't think it is simple.
For example, a route that is iced up and can be climbed as mixed ice and rock under winter conditions may be out because it is normally a trad rock climbing route.
My personal considerations are:
Is my chosen venue normally a winter venue?
Am I choosing a purely snow or ice line or are there elements of rock involved?
Are there any know ecological restrictions or issues?
Can I climb the route without crampons or using axes as balance rather than swinging axes?
How deep is the ice and snow?
Are there any exposed areas of vegetation that are unavoidable?
Personally I avoid climbing routes that are not usually winter routes. In Cwm Lloer on Monday I was able to climb on snow with a walking axe and crampons. I'm not a fan of leaving crampon or pick marks on rock if I can help it but with some routes it's the accepted norm.