Active vs. Passive voice in writing
I often find it frustrating that Word’s grammar checker always marks the passive voice as wrong. There are good and legitimate uses of the passive voice.
While it is a bit of a judgment call in academic writing a more objective tone of voice is generally appropriate. That is sometimes understood as requiring the passive voice. In a thesis or journal article the idea is to demonstrate that actions taken were based on careful research (reading, data collection, etc.) not at the whim of the researcher.
However, the passive voice can serve to obscure rather than clarify what is going on. A researcher must be careful to let the reader know who took certain actions. A description can become confusing if there are multiple researchers all referred to in the more traditional third person. In some approaches to research, ethnographic or action research for example, knowing how the research influenced the context studied helps the reader evaluate the findings and analysis of the research.
While it is designed for people writing in the sciences I have found this article from the Duke Graduate School helpful: Passive voice in scientific writing
For a briefer summary see the University of Toronto writing centre