When the topic of narrow depth of field comes up, often images that have out of focus backgrounds and bokeh balls come to mind. But like anything else, narrow depth of field can have upsides and downsides. As a result it is important to keep the impact of the selected F stop in mind, and what that will do to the plane of focus, no matter what kind of subject matter is being photographed.
For subject isolation narrow depth of field can be extremely helpful, such as with the image above that would otherwise have had a cluttered background. But what if narrow depth of field is not desirable for a particular image? Generally speaking greater depth of field can be achieved by using a larger F stop, but that does not always work. The closer the camera is to the subject matter the more difficult it becomes to achieve greater depth of field. That is also one of the positive and negative aspects of using a telephoto lens to capture a subject, as even at smaller apertures it can be difficult to gain the desired amount of in focus areas.
In the image above, the distance between the two birds is too great for both to be in focus. While this is an extreme case, due to the large gap, it demonstrates the problem. This also can be something that needs to be worked around with portraits, because if too narrow a depth of field is used one subject or part of a subject can end up being out of focus. This is often noticeable when a wide aperture lens (F2.8 or wider) is used to photograph a person from an angle, with the end result being that only one of the subjects eyes is in focus. In some situations that is acceptable, but not always.
Another area where gaining maximum depth of field can be problematic is macro photography.
As mentioned before, the closer the camera is to the subject the narrower the depth of field becomes. This can be a useful tool, such as in the image of the flower above, because the background can be softened and thus rendered in less distracting manner. Of course that same narrow plane of focus can be problematic, if it makes achieving the required depth of field needed more difficult. For that reason many macro photographers take a series of photos and combine them with the technique known as focus stacking (a technique where by a series of images are taken of the same subject, focusing on different planes of focus in order to increase the depth of field in the final combined photo).
Narrow depth of field can be an important tool for a photographer to use, but it can also be a problem to be overcome in some situations. When isolating a subject narrow depth of field can be extremely helpful, such as taking a portrait of someone in a cluttered environment. Where narrow depth of field can become troublesome is when working with telephoto lenses, or taking close up images of a flower or insect. Another setting where narrow depth of field can work against a photographer is when photographing several people or subjects that are not perfectly aligned. The bokeh that can be gained through narrow depth of field can be beautiful, but it can also be a two edged sword.