In landscape photography, of course, I try to work as low as possible, that is, ISO100. There are two reasons for this. The first reason is that large prints see grain at a higher level, and the higher it is, the more grain it will look like. The second reason is dynamic range: the higher the ISO, the shorter the dynamic range of the camera. In which ISO100 we will get the maximum dynamic range. A combination of these two factors is the reason for working at ISO100
However, there are cases in which it is impossible to avoid working at a higher level. In fact there are cases where it is absolutely necessary. The reasons for working in high photography are: Lack of light - sometimes the amount of light in the area is so small that it is impossible to photograph without some high Long Exposure - Sometimes I want to freeze the image and not make Long exposure. Not all cases exposure Long exposure to the picture Almost dark - in situations where there is still light, like the last stages of sunset, or when the sun has not yet crossed the horizon and there is not enough light. A very long exposure of a few minutes will burn pixels in the sensor, which is damage that is difficult to correct
Lack of light
Star photographs and the Milky Way are the most classic examples of the problem of landscape photography where photography is necessary at high ISO. Stars take pictures in dark conditions, otherwise we can not see enough stars. Which means that the darker the better. First of all, in the Milky Way photography we have to photograph with no exposure of more than 500/focal length, and if you want to walk on the safer side then 400/focal length. Which requires us to work at a higher ISO than usual
Milky Way photography should also work at a higher ISO than usual, and the reason is that we do not want too long exposure, otherwise we will have a graininess, or produce a print with a lot of noise. In this case it will be necessary to reduce the noise in the Lightroom, which means smoothing the picture and thereby reducing the amount of small details, which is certainly not desirable, especially if we are shooting star paths with something like a tree with small branches.
Today there seems to be a pursuit of longer and longer exposures, producing darker filters as much as possible and year after year they are darker. However, it is not always right to make long exposure, and precisely freezing objects in motion is the right thing, as in the case of the picture below. This picture was taken very early in the morning, and the sun just rose above the horizon. My problem was that it created too much darkness on the floor. If I were to shoot at a low altitude I had to smear the plane and process its beauty, or shoot at high speed and leave the floor in total darkness, and the details on the ground could not be seen. Although some high burned the sky a bit, it was made in proportion.
It's almost dark
At the end of the day the cloud formations in the sky and the movement of the trees can be perfect only when they are frozen in place. Sometimes smudging beautiful clouds, like low-altitude cumulus clouds, would mean losing their beauty, and certainly feathers in the background. The ability to describe the movement of the trees does not have to be either by smelling them. Enough to catch them frozen at the right moment.
A few last words to sum up
There is no doubt that in the last hours of the day the photographer is asked to take long exposure, whether it is the sea with the clouds being scattered, or a stream and a waterfall. But it is important to remember that the default is not automatically long exposure, and it is necessary to adjust the subject of photography to the right photography even if the price is to be higher ISO.
It is also important to remember that when you shoot at a high level there is a limit to the size of the print, and the larger the size, the smaller the size of the print.
Another thing is that when shooting at high ISO you need to increase the dynamic range in Lightroom by increasing the scale of black and white as needed
If this is the case, you should always aim to shoot at 100 ISO depending on the lighting conditions and, as far as possible, to maintain a large dynamic range and resolution