In academic reviews of this topic, the "private letter" is valued for: Authenticity

While Pen focused on adult content, the study of private letters (epistolary genre) is a serious academic field. Researchers use private letters as a to understand the intimate lives, language, and social norms of different eras.

Common motifs included "first-time" experiences, infidelity, and exploring sexual identities that were previously suppressed in Spanish media.