On that particular case, it could be considered an exploit because the player will skip a mist spawn if they're doing it at night. Could get a lot of silver back to Vallaki without any danger. For a low level char, it's not bad.
Beyond that case, I don't think a clear state on whether an area is safe or not is in any way detrimental. We should not impose cryptic rules because of a few bad players. Logging out knowing you be safe when you log in is not a luxe, it's part of a game played online.
The one case that originated this post:
I was coming back from the barataki tower when something came up IRL. I decided to go down the road a few areas, so delaying what I had to deal with OOC, to log out on a place that I supposed would be safe. I was not trying to be ported to Vallaki, and the prove is that I didn't log back until almost 24h later. I know what most of you are thinking, why not log off inside the tower? Because I guessed I had the time to go back to Vallaki, at first. When I understood I did not, I walked to the closest place with a lot of enemies. Also, it's important to note that the char was invisible and hidden, so there was a total of zero risk when I logged out.
It was very frustrating to log in without any wards in the middle of that huge battle ground.
Now that I think of it, I suppose i was still hiding when I logged on. I don't know, the whole thing made me tremble and I did click on the stealth button.
I don't see my actions as an exploit in any way, but I'm open to other interpretations.
My point is... Actually I have two points:
1. Areas should be checked for the danger tag
2. The OOC aspect of the tag should be clear. A place where there are always enemies? Dangerous, you're gonna get ported. Otherwise, you're could be in a pickle later.