The disadvantage is that the list owner loses control over who can join the list's discussions. The listserver software can keep old postings in an archive . Subscribers can send a command to listserv to get former postings. Archiving the list doesn't require effort from the list owner unless the list is moderated. Most electronic mail systems have some sort of reply command that automatically enters the sender's e-mail address when a response is made to a message.
Most systems automatically send replies to the e-mail address that sent the original message.
Unless everyone on the list is likely to have the same specific problem, the answer won't be of interest to everyone. If your list is primarily for sending information out to a group rather than for generating discussion, you might not want to have replies sent to the list. Setting replies to go to the list will increase traffic on the list, which is good if your goal is to generate discussion. A disadvantage of having replies go to the sender instead of to the list is that sometimes the reply can be of benefit to everyone. If you have replies going to the list and find that there are too many private messages, or too many messages going to the list, then it might be time for you to post a reminder to people about when to post to the list and when to post to the individual.