What is the benefit of using medium focal length lenses (80-120mm) in portrait photography?

In order to answer this question correctly, it should be further specified with information about the size of the matrix at which the object will be used. This will affect the shooting distance. With a smaller matrix, this distance will have to be greater, and with a larger matrix, shorter (while keeping the same frame). Generally speaking, a longer focal length forces you to walk away from the model and photograph e.g. from a few meters. So there is no danger of redrawing the face or figure of the photographed person. The person photographed in this way looks more natural. To illustrate this, you can imagine the opposite situation, which is photographing at close range. If you are photographing the whole person in this way (wide-angle lens), then depending on the position of the camera, you can influence the proportions of the person. You can lengthen her legs by shooting her from a low perspective, or lengthen her torso by placing the camera higher. By shooting at a greater distance, these changes are much smaller. In the case of the face, the close position of the camera introduces a disproportion between the size of what is closer to what is next. So the nose will be bigger and the ears will be smaller. The same frame taken from a greater distance (longer focal length) reduces these disproportions and the nose in relation to the ears is not so large. Thus, a longer focal length forces you to shoot at a certain distance, and this affects the presentation of more natural proportions of the subject's body. A longer focal length also reduces the depth of field, a narrower angle of observation, which results in further consequences.

In fact, a portrait can be made with any lens, from a wide angle, e.g. 14 mm, to a 200mm telephoto lens. The selection will depend on what we want to achieve. If we reach for a wide angle, we run the risk of "redrawing" the face elements closest to the lens. What is close to the glass will be magnified, what is far - much smaller. If we photograph, for example, a comedian or a clown, i.e. a sad comedian, such an exaggeration will probably be a plus. However, if we have a model or a wife in front of us :-) be careful with it. The slightly protruding nose or chin in the photo will come out even bigger. In a word, a medium focal length lens is safer in this respect, but at the same time it shortens the perspective and sometimes the oval face of the portrait subject seems flatter than it really is. The use of telephoto lenses also allows you to get a nice "bokeh", i.e. blur everything that is outside the focus zone if we use the maximum aperture. Then the portrait is isolated from the environment and we focus more attention on it, so it is safest to use something in the range of 50-85 mm, but there are no rules here, because they elude the creativity of photography

Using lenses with focal lengths of 80-120mm in portrait photography allows you to achieve natural proportions of the model's face and deep background blur, which focuses the viewer's attention on the person themselves. In addition, longer focal lengths allow for maintaining the appropriate distance between the photographer and the model, which often makes portraits more natural and lifelike.