Unlike IPR, you're never on the spot to reply immediately. You can think it through first, do a little research or soul-searching, if you wish. THEN send it off. The written dialogues of CSR may involve different mental mechanisms than in-person talk. It may reflect a distinct cognitive style that enables some people to be more expressive, subtle, organized, or creative in how they communicate.
Some people feel that they can express themselves better in the written word.
Surely, there have been truly great authors and poets who sounded bumbling or shallow during IP conversation. At your leisure, you can review what you and your partner said, cherish important moments in the relationship, and reexamine misunderstandings and conflicts. This kind of reevaluation of the relationship is impossible in IPR, where you almost always have to rely on the vagaries of memory. There are no voices, facial expressions, or body language to convey meaning and emotion. That issue takes us to the first of the five senses - hearing.