This is a good question. There are so many literary devices an author can use to achieve many different effects. If an author depicts the poem's principle action indirectly, it can achieve some interesting results. Let me mention three of them.
By describing something indirectly, a certain amount of distancing is created. There is less immediacy. There is a feeling that the material that is communicated is through the eyes or mind of another person. Hence, the material is interpreted for us.
Second, as briefly mentioned in the first point, there is issue of focalization. This is a literary device, which allows an author to see and speak through various characters. When this happens, we need to ask through whose eyes we are seeing something and how this make a difference.
Third, by making the principle action indirect, it brings the rest of the poem to the fore. It also for emphasis.