When we write a story, we decide on the genre first and then decide on the plot of the story. From that the approach we take with the story develops. That story tells us as authors whether we want to write it from a single person's point of view, alternating points of view or in third person. The story dictates whether we use flashbacks, prologues, epilogues and so forth. The story tells us whether we want to use letters, emails or journals as chapters.
It is not the reverse.
Now, in answer to this author's question, when she asked if it was a deal breaker, the answer would be one of two responses:
- Yes, if you are using a format that is not suitable to that story.
- No, if you are using a formant that IS suitable for that story.