>>2885658It really depends on subject, mood and time of day, and it seems to me that noise almost goes hand-in-hand when it comes to creating the impression of darkness, like our brains see noise and think "yeah it must have been dark there". Because I've shot night scenes on tripod at ISO100 and the cleanliness actually makes things seem slightly off or uncanny.
>>2886040I generally agree with this, but there are instances where artificial grain can be useful, although as with any effect, it needs extreme consideration before application.
The quality of the camera's own noise is fairly important, even if you leave in some luma noise, for instance I've used a 5D2 for many years and while it produced great images in good light, the noise was always poor, especially at low ISO because it took on a grid pattern more clearly.
>>2886048Not always... as I've just mentioned, certain sensors have a tendency to produce pattern noise which is constant, since the pattern is formed by the sensor's physical topology. While the 5D2 was especially notorious for this, many Canon cameras of around that time had it to varying degrees.
